When meaning matters, look but don’t touch: The effects of posture on reading

Opposing influences of global and local stimulus-hand proximity on crosstalk interference in dual tasks

In contrast to traditional dualistic views of cognition, visual stimulus processing appears not independent of bodily factors such as hand positioning. For example, reduced crosstalk between two temporally overlapping tasks has been observed when the hands are moved into the attentional window alongside their respective stimuli (i.e., establishing global stimulus-hand proximity). This result indicates that hand-specific attentional processing enhancements support a more serial rather than parallel processing of the two tasks. To further elucidate the nature of these processing modulations and their effect on multitasking performance, the present study consisted of three interrelated crosstalk experiments. Experiment 1 manipulated global stimulus-hand proximity and stimulus-effect proximity orthogonally, with results demonstrating that hand proximity rather than effect proximity drives the crosstalk reduction. Experiment 2 manipulated the physical distance between both hands (i.e., varying local stimulus-hand proximity), with results showing weak evidence of increased crosstalk when both hands are close to each other. Experiment 3 tested opposing influences of global and local stimulus-hand proximity as observed in Experiment 1 and 2 rigorously within one experiment, by employing an orthogonal manipulation of these two proximity measures. Again, we observed slightly increased crosstalk for hands close to each other (replicating Experiment 2); however, in contrast to Experiment 1, the effect of global stimulus-hand proximity on the observed crosstalk was not significant this time. Taken together, the experiments support the notion of hand-specific modulations of perception-action coupling, which can either lead to more or less interference in multitasking, depending on the exact arrangement of hands and stimuli.

Valence moderates the effect of stimulus-hand proximity on conflict processing and gaze-cueing

An effective interaction with the environment requires adaptation of one's own behaviour to environmental demands. We do so by using cues from our environment and relating these cues to our body to predict the outcomes of events. The recent literature on embodied cognition suggests that task-relevant stimuli, presented near the hands, receive more attentional capacity and are processed differently than stimuli, presented spatially more distant to our body. It has also been proposed that near-hand processing is beneficial to conflict resolution. In the current study, we tested the assumption of an attentional bias towards the near hand space in the context of our previous work by combining a cueing paradigm (allocation of visual attention) with a conflict processing paradigm (Simon task) in the near vs far hand space. In addition, the relevance of processing was manipulated by using affective (angry vs neutral smileys) gaze cues (i.e., varying the valence of the cues). Our results indicate that (a) the interaction of valence × cue congruency × hand proximity was significant, indicating that the cueing effect was larger for negative valence in the proximal condition. (b) The interaction of valence × Simon compatibility × stimulus-hand proximity interaction was significant, indicating that for negative valence processing, the Simon effect was smaller in the proximal than in the distal stimulus-hand condition. This effect was at least numerically but not significantly reversed in the neutral valence condition. (c) Overall, cue congruency, indicating the correct vs incorrect attention allocation to the target stimulus onset, did not reveal any effect on Simon compatibility × stimulus-hand proximity. Our results suggest that valence, the allocation of attention, and conflict, seem to be decisive factors determining the direction and strength of hand proximity effects.

Does hand proximity enhance letter identification?

Adam et al. (2012) found that letters were identified more accurately when presented near, compared to away from, the hands. Participants performed the task in two conditions: with their hands held stationary and with their hands moving towards and away from the target letters. The near-hands effect included the contribution of both static and dynamic trials. Further studies showed that accuracy in letter discrimination was higher when hands were away from a target (a far-hands effect) and moving toward it, suggesting an interaction between hand position and movement direction. The present study aimed to test whether hand proximity affects letter identification when the hands are stationary, as it remains unclear if this effect can be reliably observed. Participants viewed strings of three consonants, briefly presented and masked, and had to verbally report their identity. Stimuli were presented under two different hand conditions: proximal and distal. The predicted effects of letter position and stimulus duration were all statistically significant and robust; however, we did not observe a hand proximity effect.

Catch the star! Spatial information activates the manual motor system

Previous research demonstrated a close bidirectional relationship between spatial attention and the manual motor system. However, it is unclear whether an explicit hand movement is necessary for this relationship to appear. A novel method with high temporal resolution–bimanual grip force registration–sheds light on this issue. Participants held two grip force sensors while being presented with lateralized stimuli (exogenous attentional shifts, Experiment 1), left- or right-pointing central arrows (endogenous attentional shifts, Experiment 2), or the words "left" or "right" (endogenous attentional shifts, Experiment 3). There was an early interaction between the presentation side or arrow direction and grip force: lateralized objects and central arrows led to a larger increase of the ipsilateral force and a smaller increase of the contralateral force. Surprisingly, words led to the opposite pattern: larger force increase in the contralateral hand and smaller force increase in the ipsilateral hand. The effect was stronger and appeared earlier for lateralized objects (60 ms after stimulus presentation) than for arrows (100 ms) or words (250 ms). Thus, processing visuospatial information automatically activates the manual motor system, but the timing and direction of this effect vary depending on the type of stimulus.

Is semantic processing impaired near the hands?

In a sentence decision task, Davoli et al. (2010) found that the semantic analysis of sentences differed depending on whether the participants' hands were close to or far from the computer screen. According to the authors, the findings reflected an impoverishment of semantic processing near the hands. In the current study, we examine this explanation by asking whether hand position affects 1) other aspects of sentence processing, such as syntactic analysis, 2) semantic processing at the individual word level, and 3) performance in a picture naming task that requires access to meaning. In Experiment 1, participants judged the acceptability of sentences, half of which included semantic or syntactic violations. In Experiment 2, only semantically acceptable or nonacceptable sentences were presented. In Experiment 3, participants performed a go/nogo semantic categorization task on individual words. In Experiment 4, participants performed a picture naming task. Participants performed these tasks both with their hands near to and far from the computer screen. Regardless of the task, we found no evidence of impoverished semantic processing near the hands.

An auditory hand-proximity effect: The auditory Simon effect is enhanced near the hands

Visual processing near the hands is altered compared with stimuli far from the hands. Here, we aimed to test whether this alteration can be found in auditory processing. Participants were required to perform an auditory Simon task either with their hands close to the loudspeakers or far from the loudspeakers. Two experiments consistently showed that the auditory Simon effect was enhanced when the hands were close to the speakers compared with far from the speakers. This is consistent with previous findings of an enhanced visual Simon effect near the hands. Furthermore, the hand-proximity effects in auditory and visual Simon tasks (an enhanced Simon effect near hands compared with far from hands) were comparable, indicating hand-proximity effect is reliable across visual and auditory modalities. Thus, the present study extended the hand-proximity effect from vision to audition by showing that the auditory Simon effect was enhanced near the hands compared with far from the hands.

Rodin has it! The role of hands in improving the selectivity of attention

We report a new discovery on the role of hands in guiding attention, using the classic Stroop effect as our assay. We show that the Stroop effect diminishes, hence selective attention improves, when observers hold their chin, emulating Rodin's famous sculpture, "The Thinker." In two experiments we show that the Rodin posture improves the selectivity of attention as efficiently as holding the hands nearby the visual stimulus (the near-hands effect). Because spatial proximity to the displayed stimulus is neither present nor intended, the presence of the Rodin effect implies that attentional prioritization by the hands is not limited to the space between the hands.

The Impact of a Self-Avatar, Hand Collocation, and Hand Proximity on Embodiment and Stroop Interference

Understanding the effects of hand proximity to objects and tasks is critical for hand-held and near-hand objects. Even though self-avatars have been shown to be beneficial for various tasks in virtual environments, little research has investigated the effect of avatar hand proximity on working memory. This paper presents a between-participants user study investigating the effects of self-avatars and physical hand proximity on a common working memory task, the Stroop interference task. Results show that participants felt embodied when a self-avatar was in the scene, and that the subjective level of embodiment decreased when a participant's hands were not collocated with the avatar's hands. Furthermore, a participant's physical hand placement was significantly related to Stroop interference: proximal hands produced a significant increase in accuracy compared to non-proximal hands. Surprisingly, Stroop interference was not mediated by the existence of a self-avatar or level of embodiment.

Prolonged subjective duration near the hands: Effects of hand proximity on temporal reproduction

It has been reported that human visual perception and attention are altered when the hands are nearby. Previous studies indicate that placing hands near stimuli enhances a subject's temporal sensitivity. However, few researchers have investigated the effect of hand proximity on reproducing temporal duration. Moreover, the delayed attentional disengagement and enhanced magnocellular visual processing theories provide two distinct predictions of the hand proximity effect on reproduced duration. Delayed attentional disengagement near hands will cause prolonged reproductions, whereas enhanced magnocellular visual processing predicts more accurate reproduction in the peri-hand space. The current study is the first to show that a short temporal duration is reproduced for a longer period near hands than far from hands in the dual-responding-hand condition, and this hand-proximity effect is attenuated in the single-responding-hand condition. These findings together with two further studies suggest that reproducing a temporal duration is modulated by hand proximity through prolonged attentional switch.

Embodied cognition in multitasking: increased hand-specific task shielding when stimuli are presented near the hand

The proximity of hand position alters the processing of visual stimuli. Stimuli presented close (proximal) to hands receive an enhanced allocation of visual attention compared to stimuli presented far (distal) from hands. In the present dual-task study we studied the consequences of this preferential processing when the stimulus for Task 1 (S1) and the stimulus for Task 2 (S2) were presented together and were assigned to specific response hands (R1 and R2) located proximal (at the monitor) versus distal (in the lap) to the stimuli. In two experiments, we tested whether stimulus-hand proximity affected the extent of between-task interference (i.e., influence of additional Task 2 processing on primary Task 1 processing). In Experiment 1, results showed that stimulus-hand proximity reduced the amount of between-task interference compared to the distal stimulus-hand condition. Extending these findings, in Experiment 2 a further reduction of between-task interference was obtained when a single hand was located at the monitor instead of two hands. These results are inconsistent with the assumption of a generally increased attentional processing benefit for multiple stimuli within hand space. Instead, these findings speak for a hand-specific processing benefit that supports more separate processing of two tasks. Together these findings demonstrate that stimulus-hand proximity affects the quality of multiple task performance, which is discussed in the context of both, basic and applied cognitive research.

Dual-Tasking in the Near-Hand Space: Effects of Stimulus-Hand Proximity on Between-Task Shifts in the Psychological Refractory Period Paradigm

Two decades of research indicate that visual processing is typically enhanced for items that are in the space near the hands (near-hand space). Enhanced attention and cognitive control have been thought to be responsible for the observed effects, amongst others. As accumulating experimental evidence and recent theories of dual-tasking suggest an involvement of cognitive control and attentional processes during dual tasking, dual-task performance may be modulated in the near-hand space. Therefore, we performed a series of three experiments that aimed to test if the near-hand space affects the shift between task-component processing in two visual-manual tasks. We applied a Psychological Refractory Period Paradigm (PRP) with varying stimulus-onset asynchrony (SOA) and manipulated stimulus-hand proximity by placing hands either on the side of a computer screen (near-hand condition) or on the lap (far-hand condition). In Experiment 1, Task 1 was a number categorization task (odd vs. even) and Task 2 was a letter categorization task (vowel vs. consonant). Stimulus presentation was spatially segregated with Stimulus 1 presented on the right side of the screen, appearing first and then Stimulus 2, presented on the left side of the screen, appearing second. In Experiment 2, we replaced Task 2 with a color categorization task (orange vs. blue). In Experiment 3, Stimulus 1 and Stimulus 2 were centrally presented as a single bivalent stimulus. The classic PRP effect was shown in all three experiments, with Task 2 performance declining at short SOA while Task 1 performance being relatively unaffected by task-overlap. In none of the three experiments did stimulus-hand proximity affect the size of the PRP effect. Our results indicate that the switching operation between two tasks in the PRP paradigm is neither optimized nor disturbed by being processed in near-hand space.

Building Blocks of Psychology: on Remaking the Unkept Promises of Early Schools

The appeal and popularity of "building blocks", i.e., simple and dissociable elements of behavior and experience, persists in psychological research. We begin our assessment of this research strategy with an historical review of structuralism (as espoused by E. B. Titchener) and behaviorism (espoused by J. B. Watson and B. F. Skinner), two movements that held the assumption in their attempts to provide a systematic and unified discipline. We point out the ways in which the elementism of the two schools selected, framed, and excluded topics of study. After the historical review, we turn to contemporary literature and highlight the persistence of research into building blocks and the associated framing and exclusions in psychological research. The assumption that complex categories of human psychology can be understood in terms of their elementary components and simplest forms seems indefensible. In specific cases, therefore, reliance on the assumption requires justification. Finally, we review alternative strategies that bypass the commitment to building blocks.

Impaired conflict monitoring near the hands: Neurophysiological evidence

Recent evidence suggests that hand-stimulus proximity enhances the visuo-motor Simon effect. The present study used event-related potentials (ERP) to examine the timing at which hand-stimulus proximity modulates the Simon effect. The results show that the P1 and N1 components were not modulated by hand-stimulus proximity, suggesting that early sensory processing is not altered by hand-stimulus proximity. However, the interference effect (the difference between incompatible versus compatible trials) on the N2 component was significantly attenuated near the hands compared to far from the hands, indicating that hand-stimulus proximity impairs conflict monitoring. We also found significant effects on a later component, as the P3 was reduced and had a shorter latency for the hand-proximal condition relative to the hand-distal condition. These new findings suggest that the critical stage at which hand-stimulus proximity affects cognitive processing lies past the early perceptual processing, acting instead on later stages of processing related to executive functioning.

The Fragility of the Near-Hand Effect

Recent literature has demonstrated that hand position can affect visual processing, a set of phenomena termed Near Hand Effects (NHEs). Across four studies we looked for single-hand NHEs on a large screen when participants were asked to discriminate stimuli based on size, colour, and orientation (Study 1), to detect stimuli after a manipulation of hand shaping (Study 2), to detect stimuli after the introduction of a peripheral cue (Study 3), and finally to detect stimuli after a manipulation of screen orientation (Study 4). Each study failed to find a NHE. Further examination of the pooled data using a Bayesian analysis also failed to reveal positive evidence for faster responses or larger cueing effects near a hand. These findings suggest that at least some NHEs may be surprisingly fragile, which dovetails with the recent proposition that NHEs may not form a unitary set of phenomena (Gozli & Deng, 2018). The implication is that visual processing may be less sensitive to hand position across measurement techniques than previously thought, and points to a need for well-powered, methodologically rigorous studies on this topic in the future.

Immobilization does not disrupt near-hand attentional biases

Observers show biases in attention when viewing objects within versus outside of their hands' grasping space. While the hands' proximity to stimuli plays a key role in these effects, recent evidence suggests an observer's affordances for grasping actions also shape visual processing near the hands. The current study examined the relative contributions of proximity and affordances in introducing attentional biases in peripersonal space. Participants placed a single hand on a visual display and detected targets appearing near or far from the hand. Across conditions, the hand was either free, creating an affordance for a grasping action, or immobilized using an orthosis, interfering with the potential to grasp. Replicating previous findings, participants detected targets appearing near the hand more quickly than targets appearing far from the hand. Immobilizing the hands did not disrupt this effect, suggesting that proximity alone is sufficient to facilitate target detection in peripersonal space.

Hand proximity effects are fragile: a useful null result

Placing one’s hands near an object has been reported to enhance visual processing in a number of ways. We explored whether hand proximity confers an advantage when applied to complex visual search. In one experiment, participants indicated the presence or absence of a target item in a baggage x-ray image by pressing response boxes located at the edge of a tablet computer screen, requiring them to grip the display between their hands. Alternatively, they responded using a mouse held within their lap. Contrary to expectations, hand position did not influence search performance. In a second experiment, participants used their finger to trace along the x-ray image while searching. In addition to any effect of hand proximity it was predicted that this strategy would encourage a more systematic search strategy. Participants inspected bags longer using this strategy, but this did not translate into improved target detection. A third experiment attempted to replicate the near-hands advantage in a change detection paradigm featuring simple stimuli (Tseng and Bridgeman, Experimental Brain Research 209:257–269, 2011), and the same equipment and hand positions as Experiment 1, but was unable to do so. One possibility is that the grip posture associated with holding a tablet is not conducive to producing a near-hands advantage. A final experiment tested this hypothesis with a direct replication of Tseng and Bridgeman, in which participants responded to stimuli presented on a CRT monitor using keys attached to the side of the monitor. Still, no near-hands advantage was observed. Our results suggest that the near-hands advantage may be sensitive to small differences in procedure, a finding that has important implications for harnessing the near-hands advantage to produce better performance in applied contexts.

Slower attentional disengagement but faster perceptual processing near the hand

Many recent studies have reported altered visual processing near the hands. However, there is no definitive agreement about the mechanisms responsible for this effect. One viewpoint is that the effect is predominantly attentional while others argue for the role of pre-attentive perceptual differences in the manifestation of the hand-proximity effect. However, in most of the studies pre-attentional and attentional effects have been conflated. We argue that it is important to dissociate the effect of hand proximity on perception and attention to better theorize and understand how visual processing is altered near the hands. We report two experiments using a visual search task where participants completed a visual search task with their hands either on the monitor or on their lap. When on the monitor, the target could appear near the hand or farther away. In experiment 1, a letter search task showed steeper search slope near the hand suggesting slower attentional disengagement. However, the intercept was smaller in the near hand condition suggesting faster perceptual processing. These results were also replicated in experiment 2 with a conjunction search task with target present and absent conditions and 4 set sizes. The results suggest that there are dissociable effects of hand proximity on perception and attention. Importantly, the pre-attentive advantage of hand proximity does not translate to attentional benefit, but a processing cost. The results of experiment 2 additionally indicate that the steeper slope does not arise from any spatial biases in how search proceeds, but an indicator of slower attentional processing near the hands. The results also suggest that the effect of hand proximity on attention is not spatially graded whereas its effect on perceptuo-motor processes seems to be.

Handedness and Graspability Modify Shifts of Visuospatial Attention to Near-Hand Objects

We examined how factors related to the internal representation of the hands (handedness and grasping affordances) influence the distribution of visuospatial attention near the body. Left and right handed participants completed a covert visual cueing task, discriminating between two target shapes. In Experiment 1, participants responded with either their dominant or non-dominant hand. In Experiment 2, the non-responding hand was positioned below one of two target placeholders, aligned with the shoulder. In Experiment 3 the near-monitor hand was positioned under the placeholder in the opposite region of hemispace, crossed over the body midline. For Experiments 2 & 3, in blocked trials the palmar and back-of hand surfaces were directed towards the target placeholder such that targets appeared towards either the graspable or non-graspable space of the hand respectively. In Experiment 2, both left and right handers displayed larger accuracy cueing effects for targets near versus distant from the graspable space of the right hand. Right handers also displayed larger response time cueing effects for objects near the graspable versus non-graspable region of their dominant hand but not for their non-dominant hands. These effects were not evident for left-handers. In Experiment 3, for right handers, accuracy biases for near hand targets were still evident when the hand was crossed over the body midline, and reflected hand proximity but not functional orientation biases. These findings suggest that biased visuospatial attention enhances object identity discrimination near hands and that these effects are particularly enhanced for right-handers.

Syntax response-space biases for hands, not feet

A number of studies have shown a relationship between comprehending transitive sentences and spatial processing (e.g., Chatterjee, Trends in Cognitive Sciences, 5(2), 55-61, 2001), in which there is an advantage for responding to images that depict the agent of an action to the left of the patient. Boiteau and Almor (Cognitive Science, 2016) demonstrated that a similar effect is found for pure linguistic information, such that after reading a sentence, identifying a word that had appeared earlier as the agent is faster on the left than on the right, but only for left-hand responses. In this study, we examined the role of lateralized manual motor processes in this effect and found that such spatial effects occur even when only the responses, but not the stimuli, have a spatial dimension. In support of the specific role of manual motor processes, we found a response-space effect with manual but not with pedal responses. Our results support an effector-specific (as opposed to an effector-general) hypothesis: Manual responses showed spatial effects compatible with those in previous research, whereas pedal responses did not. This is consistent with theoretical and empirical work arguing that the hands are generally involved with, and perhaps more sensitive to, linguistic information.

Effects of Hand Proximity and Movement Direction in Spatial and Temporal Gap Discrimination

Previous research on the interplay between static manual postures and visual attention revealed enhanced visual selection near the hands (near-hand effect). During active movements there is also superior visual performance when moving toward compared to away from the stimulus (direction effect). The “modulated visual pathways” hypothesis argues that differential involvement of magno- and parvocellular visual processing streams causes the near-hand effect. The key finding supporting this hypothesis is an increase in temporal and a reduction in spatial processing in near-hand space (Gozli et al., 2012). Since this hypothesis has, so far, only been tested with static hand postures, we provide a conceptual replication of Gozli et al.’s (2012) result with moving hands, thus also probing the generality of the direction effect. Participants performed temporal or spatial gap discriminations while their right hand was moving below the display. In contrast to Gozli et al. (2012), temporal gap discrimination was superior at intermediate and not near hand proximity. In spatial gap discrimination, a direction effect without hand proximity effect suggests that pragmatic attentional maps overshadowed temporal/spatial processing biases for far/near-hand space.

Task demands determine hand posture bias on conflict processing in a Simon task

A huge body of research in humans and monkeys has provided evidence for altered processing of items that are presented close to the hands. At the same time, the underlying mechanisms that explain why objects close to the hands are processed differently from objects far from the hands are still debated. Empirical demonstrations have provided evidence for the involvement of bottom-up influences, but also for top-down influences of task relevance. Objects close to the hands change spatial attentional processing or are subject to increased cognitive control. The present study demonstrated that variations in the task-processing demands predicted the hand posture influence on conflict resolution in a Simon task. Participants responded with their hands either at the monitor (close to the stimuli) or on their knees (far from the stimuli). The Simon effect was significantly reduced for the hands-close as compared to the hands-far condition when participants performed a numerical size judgment (Exps. 1 and 2). In contrast, the Simon effect was significantly increased for the hands-close condition when the Simon task consisted of a low-level perceptual feature discrimination (i.e., color task, Exp. 2). The obtained task-processing specificity provides further evidence that a highly flexible system underlies hand posture effects on stimulus processing.

Action Experience Drives Visual-Processing Biases Near the Hands

Observers experience affordance-specific biases in visual processing for objects within the hands' grasping space, but the mechanism that tunes visual cognition to facilitate action remains unknown. I investigated the hypothesis that altered vision near the hands is a result of experience-driven plasticity. Participants performed motion-detection and form-perception tasks-while their hands were either near the display, in atypical grasping postures, or positioned in their laps-both before and after learning novel grasp affordances. Participants showed enhanced temporal sensitivity for stimuli viewed near the backs of the hands after training to execute a power grasp using the backs of their hands (Experiment 1), but showed enhanced spatial sensitivity for stimuli viewed near the tips of their little fingers after training to use their little fingers to execute a precision grasp (Experiment 2). These results show that visual biases near the hands are plastic, facilitating processing of information relevant to learned grasp affordances.

The nature of altered vision near the hands: evidence for the magnocellular enhancement account from object correspondence through occlusion

A growing body of evidence indicates that the perception of visual stimuli is altered when they occur near the observer's hands, relative to other locations in space (see Brockmole, Davoli, Abrams, & Witt, 2013, for a review). Several accounts have been offered to explain the pattern of performance across different tasks. These have typically focused on attentional explanations (attentional prioritization and detailed attentional evaluation of stimuli in near-hand space), but more recently, it has been suggested that near-hand space enjoys enhanced magnocellular (M) input. Here we differentiate between the attentional and M-cell accounts, via a task that probes the roles of position consistency and color consistency in determining dynamic object correspondence through occlusion. We found that placing the hands near the visual display made observers use only position consistency, and not color, in determining object correspondence through occlusion, which is consistent with the fact that M cells are relatively insensitive to color. In contrast, placing observers' hands far from the stimuli allowed both color and position contribute. This provides evidence in favor of the M-cell enhancement account of altered vision near the hands.

Hand posture and cognitive control: The congruency sequence effect is reduced near the hands

According to several recent articles, attentional processing seems to be modulated by the proximity of one's own hand to a stimulus. Weidler and Abrams (Psychonomic Bulletin & Review, 21, 462-469, 2014) found a significant reduction of the Eriksen flanker effect when the stimuli were presented close to the participants' hands. They interpreted this as evidence for stronger cognitive control near the hands. Using a near-by hands manipulation intended to vary distance while keeping posture of the hands constant, we found a modulation of the congruency sequence effect (CSE or Gratton effect), i.e., a larger flanker effect following incompatible trials than following compatible trials. The CSE was eliminated near the hands. Though we did not find a reduction in the flanker effect itself (which might be the result of using a near-by hand manipulation somewhat different from that of Weidler and Abrams), this result can be considered to be compatible with Weidler and Abrams' original hypothesis if the congruency sequence effect is interpreted in terms of cognitive control.

Reduced object-based perception in the near-hand space

Previous studies have shown that hand proximity changes visual perception (Abrams et al. in Cognition 107(3):1035-1047, 2008). The present study examined the effects of hand proximity on object-based perception. In three experiments, participants viewed stimuli that were either near to or far from their hands. The target stimulus appeared, after a cue, in one of two rectangular objects: either at the location that had been previously cued, at the uncued end of the cued object, or in the uncued object. We found a significantly reduced same-object benefit in reaction time for stimuli near the hands in one experiment. Interestingly, we observed a same-object cost in sensitivity for stimuli near the hands in another experiment. The results reveal that object-based perception is disrupted in the near-hand space. This is consistent with previous findings revealing altered visual processing near the hands.

Exogenous and endogenous shifts of attention in perihand space

While some studies have found that attentional orienting is altered in perihand space, most have not. One reason for such discrepancies may be related to the types of cues (uninformative and informative) that have been used, as they are known to induce different types of shifts of attention (exogenous and endogenous, respectively). To systematically address this question, two experiments were performed in which an uninformative peripheral cue (Experiment 1) or an informative central cue (Experiment 2) preceded a peripheral target with a short (100-150 ms) stimulus-onset asynchrony. Participants performed the task with their left hand, right hand, both hands, or no hands near the display. Cueing effects were obtained in both experiments, but they were only modulated by hand position in Experiment 1, with larger effects observed in the right- and both-hand conditions. These findings suggest that exogenous attention shifts are affected by hand proximity, while endogenous shifts are not.

Hand position influences perceptual grouping

Over the past decade, evidence has accumulated that performance in attention, perception, and memory-related tasks are influenced by the distance between the hands and the stimuli (i.e., placing the observer's hands near or far from the stimuli). To account for existing findings, it has recently been proposed that processing of stimuli near the hands is dominated by the magnocellular visual pathway. The present study tests an implication of this hypothesis, whether perceptual grouping is reduced in hands-proximal space. Consistent with previous work on the object-based capture of attention, a benefit for the visual object in the hands-distal condition was observed in the present study. Interestingly, the object-based benefit did not emerge in the hands-proximal condition, suggesting perceptual grouping is impaired near the hands. This change in perceptual grouping processes provides further support for the hypothesis that visual processing near the hands is subject to increased magnocellular processing.

Interacting hands: the role of attention for the joint Simon effect

Recent research in monkeys and humans has shown that the presence of the hands near an object enhances spatial processing for objects presented near the hand. This study aimed to test the effect of hand position on the joint Simon effect. In Experiment 1, two human co-actors shared a Simon task while placing their response hands either near the objects appearing on the monitor or away from the monitor. Experiment 2 varied each co-actor’s hand position independently. Experiment 3 tested whether enhanced spatial processing for objects presented near the hand is obtained when replacing one of the two co-actors by a non-human event-producing rubber hand. Experiment 1 provided evidence for a Simon effect. Hand position significantly modulated the size of the Simon effect in the joint Simon task showing an increased Simon effect when the hands of both actors were located near the objects on the monitor, than when they were located away from the monitor. Experiment 2 replicated this finding showing an increased Simon effect when the actor’s hand was located near the objects on the monitor, but only when the co-actor also produced action events in spatial reference. A similar hand position effect was observed in Experiment 3 when a non-human rubber hand replaced the human co-actor. These findings suggest that external action events that are produced in spatial reference bias the distribution of attention to the area near the hand. This strengthens the weight of the spatial response codes (referential coding) and hence increases the joint Simon effect.

A touchy subject: advancing the modulated visual pathways account of altered vision near the hand

A growing body of evidence demonstrates that human vision operates differently in the space near and on the hands; for example, early findings in this literature reported that rapid onsets are detected faster near the hands, and that objects are searched more thoroughly. These and many other effects were attributed to enhanced attention via the recruitment of bimodal visual-tactile neurons representing the hand and near-hand space. However, recent research supports an alternative account: stimuli near the hands are preferentially processed by the action-oriented magnocellular visual pathway at the expense of processing in the parvocellular pathway. This Modulated Visual Pathways (MVP) account of altered vision near the hands describes a hand position-dependent trade-off between the two main retinal-cortical visual pathways between the eye and brain. The MVP account explains past findings and makes new predictions regarding near-hand vision supported by new research.

Trade-offs in visual processing for stimuli near the hands

It is known that stimuli near the hands receive preferential processing. In the present study, we explored changes in early vision near the hands. Participants were more sensitive to low-spatial-frequency information and less sensitive to high-spatial-frequency information for stimuli presented close to the hands. This pattern suggests enhanced processing in the magnocellular visual pathway for such stimuli, and impaired processing in the parvocellular pathway. Consistent with that possibility, we found that the effects of hand proximity in several tasks were eliminated by illumination with red diffuse light-a manipulation known to impair magnocellular processing. These results help clarify how the hands affect vision.

Hand proximity facilitates spatial discrimination of auditory tones

The effect of hand proximity on vision and visual attention has been well documented. In this study we tested whether such effect(s) would also be present in the auditory modality. With hands placed either near or away from the audio sources, participants performed an auditory-spatial discrimination (Experiment 1: left or right side), pitch discrimination (Experiment 2: high, med, or low tone), and spatial-plus-pitch (Experiment 3: left or right; high, med, or low) discrimination task. In Experiment 1, when hands were away from the audio source, participants consistently responded faster with their right hand regardless of stimulus location. This right hand advantage, however, disappeared in the hands-near condition because of a significant improvement in left hand's reaction time (RT). No effect of hand proximity was found in Experiments 2 or 3, where a choice RT task requiring pitch discrimination was used. Together, these results that the perceptual and attentional effect of hand proximity is not limited to one specific modality, but applicable to the entire “space” near the hands, including stimuli of different modality (at least visual and auditory) within that space. While these findings provide evidence from auditory attention that supports the multimodal account originally raised by Reed et al. (2006), we also discuss the possibility of a dual mechanism hypothesis to reconcile findings from the multimodal and magno/parvocellular account.

Hand proximity differentially affects visual working memory for color and orientation in a binding task

Observers determined whether two sequentially presented arrays of six lines were the same or different. Differences, when present, involved either a swap in the color of two lines or a swap in the orientation of two lines. Thus, accurate change detection required the binding of color and orientation information for each line within visual working memory. Holding viewing distance constant, the proximity of the arrays to the hands was manipulated. Placing the hands near the to-be-remembered array decreased participants’ ability to remember color information, but increased their ability to remember orientation information. This pair of results indicates that hand proximity differentially affects the processing of various types of visual information, a conclusion broadly consistent with functional and anatomical differences in the magnocellular and parvocellular pathways. It further indicates that hand proximity affects the likelihood that various object features will be encoded into integrated object files.

Determinants of attentional modulation near the hands

A series of visual search experiments conducted by Abrams et al. (2008) indicates that disengagement of visual attention is slowed when the array of objects that are to be searched are close to the hands (hands on the monitor) than if they are not close to the hands (hands in the lap). These experiments establish the impact one's hands can have on visual attentional processing. In the current paper we more closely examine these two hand postures with the goal of pinpointing which characteristics are crucial for the observed differences in attentional processing. Specifically, in a set of 4 experiments we investigated additional hand postures and additional modes of response to address this goal. We replicated the original Abrams et al. (2008) effect when only the two original postures were used; however, surprisingly, the effect was extinguished with the new range of postures and response modes, and this extinction persisted across different populations (German and English students), and different experimental hardware. Furthermore, analyses indicated that it is unlikely that the extinction of the effect was caused by increased practice due to additional blocks of trials or by an increased probability that participants were able to guess the purpose of the experiment. As such our results suggest that in addition to the nature of the postures of the hand, the number of postures is a further important factor that influences the impact the hands have on visual processing.

Shorter lines facilitate reading in those who struggle

People with dyslexia, who ordinarily struggle to read, sometimes remark that reading is easier when e-readers are used. Here, we used eye tracking to observe high school students with dyslexia as they read using these devices. Among the factors investigated, we found that reading using a small device resulted in substantial benefits, improving reading speeds by 27%, reducing the number of fixations by 11%, and importantly, reducing the number of regressive saccades by more than a factor of 2, with no cost to comprehension. Given that an expected trade-off between horizontal and vertical regression was not observed when line lengths were altered, we speculate that these effects occur because sluggish attention spreads perception to the left as the gaze shifts during reading. Short lines eliminate crowded text to the left, reducing regression. The effects of attention modulation by the hand, and of increased letter spacing to reduce crowding, were also found to modulate the oculomotor dynamics in reading, but whether these factors resulted in benefits or costs depended on characteristics, such as visual attention span, that varied within our sample.

How action influences object perception

Although object perception is typically associated with the parvocellular (P) pathway, a form of fast "gist" object perception may be due to activity in the magnocellular (M) pathway (Kveraga et al., 2007). Because the M-pathway is typically associated with action, we hypothesized that manipulations of action would influence speeded object perception. In three experiments, participants indicated whether the objects shown in low and high spatial frequency (HSF) images were larger or smaller than a prototypical shoebox. In Experiment 1, participants used a proximal (hands on monitor) or distal (hands on keyboard) hand posture in separate blocks. In Experiment 2, only the proximal hand posture was used, but the hands were either action oriented with palms in (palms toward the stimuli) or non-action oriented with palms out (palms away from the stimuli). In Experiment 3, we used the palms-in proximal hand posture but manipulated the type of visual stimuli such that they were either action oriented (easily grasped) or non-action oriented (not easily grasped). In all three experiments, the advantage in identifying the low spatial frequency (LSF) images was greater when action was primed (proximal hands, palms-in, graspable). Together, these experiments show that the M-pathway is involved in rapid "gist" object perception, and this type of object perception is influenced by action.

Biased attention near another's hand following joint action

Previous research has shown that attention is prioritized for the space near the hand, leading to faster detection of visual targets appearing close to one's own hand. In the present study, we examined whether observers are also facilitated in detecting targets presented near another's hand by having participants perform a Posner cueing task while sitting next to a friend. Across blocks, either the participant or the friend placed a hand next to one of the target locations. Our results robustly showed that participants detected targets appearing near their own hands more quickly than targets appearing away from their hands, replicating previous work demonstrating that spatial attention is prioritized near one's own hand (Experiments 1-4). No such attentional bias effects were found for targets appearing near the friend's hand, suggesting that spatial attention is not automatically prioritized near another's hand (Experiments 1 and 2). However, participants were faster to detect targets near the friend's hand following a joint action task, suggesting a shared body representation plays an influential role in biasing attention to the space near another's hand (Experiment 4).

Reduced Temporal Fusion in Near-Hand Space

Object-substitution masking (OSM) is thought to reflect a failure of object individuation. That is, a briefly presented target surrounded by four dots is perceptually fused with the four-dot mask when the mask is visible after the target has disappeared, thereby obscuring the visibility of the target. If OSM depends on the inability to temporally segregate objects, then increasing the temporal precision of the visual system should reduce OSM. In the study reported here, we manipulated temporal precision by varying the proximity of participants’ hands to visual stimuli, because stimuli in near-hand space have been found to enjoy enhanced attentional processing, and attention is known to speed visual processing. Hand placement was indeed found to affect OSM: Placing participants’ hands near the visual stimuli reduced the magnitude of the masking. This finding demonstrates that object individuation can be facilitated by increasing the temporal resolution of vision via increasing the proximity of visual stimuli to the hands.