Attention can retrospectively distort visual space

Examining the Impact of Human Face Stimulus on Shape-Contrast Effects during a Brief Presentation

Shape-contrast effects have been introduced to the investigations into face perception with the aim of exploring face adaptation in the context of norm-based coding. Research has indicated that shape-contrast effects occur even for shapes as complex as the human face. However, whether the complexity of face stimuli alters the magnitude of shape-contrast effects needs to be examined. In this study, emoticons and realistic human faces were used with the original white circle as the test stimuli. The results revealed that the shape-contrast effect was dependent on the stimulus. However, there was no significant difference between the shape-contrast effect evoked by upright faces and that evoked by inverted ones. This suggests that the face stimuli influenced the strength of the shape-contrast effect: the mechanism of this effect involved multiple stages of the visual system related to luminance and complexity, rather than the holistic face perception.

Temporal context affects the perceived time of visual events

We investigated whether the moment at which an event is perceived depends on its temporal context. Participants learned a mapping between time and space by watching the hand of a clock rotating a full revolution in a fixed duration. Then the hand was removed, and a target disc was flashed within a fixed-interval duration. Participants were to indicate where the hand would have been at the time of the target. In three separate experiments, we estimated the disruption from a distractor disc that was presented before or after the target disc, with a variable time between them. The target was either revealed at the end of the trial or cued beforehand, and in the latter case, was cued by either color or temporal order. We found an attraction to the presentation time of the distractor when both events were attended equally (target revealed at the end). When the target was cued beforehand, the reported time was under- or overestimated, depending on whether the nature of distractor had to be decoded (precued by color) or not (precued by order). In summary, the perceived time of an event is always affected by other events in temporal proximity, but the nature of this effect depends on how each event is attended.

Vertical and horizontal meridian modulations suggest areas with quadrantic representations as neural locus of the attentional repulsion effect

The attentional repulsion effect (ARE) is a perceptual bias attributed to a covert shift of attention toward a peripheral cue, which, in turn, repulses the perceived position of a subsequently presented probe (Suzuki & Cavanagh, 1997). So far, probes were mainly presented around the vertical meridian. Other studies of perceptual biases reported disruptions when stimuli were presented across the vertical meridian. These disruptions were explained by separate representations of the left and right visual hemifields, projecting to opposite anatomical hemispheres. As the ARE is typically examined through two-alternative, forced-choice tasks in which the estimation of the probe's position is based on the cue's effectiveness to repulse the probe across the vertical meridian, no such asymmetry has been reported. To test for similar meridian disruptions in the ARE, we collected absolute estimations (computer mouse responses) of the perceived probe positions (Experiment 1a). As absolute estimations of memorized positions are associated with overestimated distances in reproduction, results had to be compared to a no-cue baseline condition (Experiment 1b). Through this new methodological approach, we found the ARE to be strongest when the attentional capturing cue and the subsequently presented probe were displayed in the same hemifield (Experiment 2a). In a further experiment (Experiment 2b), we observed that the ARE is not only disrupted at the vertical, but also at the horizontal meridian. These disruptions at both meridians suggest the involvement of visual neural areas with quadrantic representations, such as V2 and/or V3 in the generation of the ARE.

Independent working memory resources for egocentric and allocentric spatial information

Visuospatial working memory enables us to maintain access to visual information for processing even when a stimulus is no longer present, due to occlusion, our own movements, or transience of the stimulus. Here we show that, when localizing remembered stimuli, the precision of spatial recall does not rely solely on memory for individual stimuli, but additionally depends on the relative distances between stimuli and visual landmarks in the surroundings. Across three separate experiments, we consistently observed a spatially selective improvement in the precision of recall for items located near a persistent landmark. While the results did not require that the landmark be visible throughout the memory delay period, it was essential that it was visible both during encoding and response. We present a simple model that can accurately capture human performance by considering relative (allocentric) spatial information as an independent localization estimate which degrades with distance and is optimally integrated with egocentric spatial information. Critically, allocentric information was encoded without cost to egocentric estimation, demonstrating independent storage of the two sources of information. Finally, when egocentric and allocentric estimates were put in conflict, the model successfully predicted the resulting localization errors. We suggest that the relative distance between stimuli represents an additional, independent spatial cue for memory recall. This cue information is likely to be critical for spatial localization in natural settings which contain an abundance of visual landmarks.

On spatial attention and its field size on the repulsion effect

We investigated the attentional repulsion effect-stimuli appear displaced further away from attended locations-in three experiments: one with exogenous (involuntary) attention, and two with endogenous (voluntary) attention with different attention-field sizes. It has been proposed that differences in attention-field size can account for qualitative differences in neural responses elicited by attended stimuli. We used psychophysical comparative judgments and manipulated either exogenous attention via peripheral cues or endogenous attention via central cues and a demanding rapid serial visual presentation task. We manipulated the attention field size of endogenous attention by presenting streams of letters at two specific locations or at two of many possible locations during each block. We found a robust attentional repulsion effect in all three experiments: with endogenous and exogenous attention and with both attention-field sizes. These findings advance our understanding of the influence of spatial attention on the perception of visual space and help relate this repulsion effect to possible neurophysiological correlates.

Numerical value biases sound localization

Speech recognition starts with representations of basic acoustic perceptual features and ends by categorizing the sound based on long-term memory for word meaning. However, little is known about whether the reverse pattern of lexical influences on basic perception can occur. We tested for a lexical influence on auditory spatial perception by having subjects make spatial judgments of number stimuli. Four experiments used pointing or left/right 2-alternative forced choice tasks to examine perceptual judgments of sound location as a function of digit magnitude (1–9). The main finding was that for stimuli presented near the median plane there was a linear left-to-right bias for localizing smaller-to-larger numbers. At lateral locations there was a central-eccentric location bias in the pointing task, and either a bias restricted to the smaller numbers (left side) or no significant number bias (right side). Prior number location also biased subsequent number judgments towards the opposite side. Findings support a lexical influence on auditory spatial perception, with a linear mapping near midline and more complex relations at lateral locations. Results may reflect coding of dedicated spatial channels, with two representing lateral positions in each hemispace, and the midline area represented by either their overlap or a separate third channel.

[Sequential effect in attractiveness judgement of multiple faces]

A large number of studies have demonstrated the sequential effect, in which the response in the current trial is assimilated towards that of the immediately preceding trial in a decision making task. However, most previous studies have only examined the effect in situations where the response was given after each stimulus presentation. In this study, we examined whether the sequential effect existed when observers responded after the presentation of two stimuli. After two pictures of male faces were presented successively, participants rated the attractiveness of each face on a 9-point scale. The results showed that the second response was assimilated towards the first (Experiment 1), but the first response contrasted with (shifted away from) the second (Experiment 2). These findings suggest that preceding and succeeding contexts may differentially modulate our decision making.

Examining the locus of the attentional attraction effect

Our spatial perception is not always veridical. Indeed, systematic distortions in localization have been found to result from orienting of attention. Distorted localization is inferred from tasks wherein the subject reports the location of centrally presented parallel (vernier) line stimuli. Particularly, prior to the presentation of the lines, a shift of attention toward peripheral cues produces a mislocalization of the line stimuli away from the cues (termed the attentional repulsion effect [ARE]). However, if the shift of attention is induced after target presentation, by reversing the order of stimulus presentation, a substantial mislocalization toward the cues (attentional attraction effect [AAE]) is found. The purpose of this study was to identify whether the AAE arises from the modulation in the same processes as the ARE. While an interocular presentation of cues to one eye and vernier lines to the other was previously shown to eliminate the ARE, the AAE persists across both the interocular and monocular conditions (both the cues and vernier lines are presented to the same eye). Considering Ono and Watanabe's (2011) suggestion that memory traces may be involved in generating the AAE, this prospect was examined by having participants delay their response for a short (100 ms) or long (1,000 ms) period of time. The magnitude of AAE was larger with a longer delay, consistent with the involvement of visual memory. Next, to directly examine the role of spatial working memory, the attentional attraction task was embedded within either a spatial memory task (remembering the locations of one or three squares) or a color memory task (remembering the color of one or three squares). Only high spatial memory load reduced the magnitude of AAE. Our results suggest the AAE relies on changes to different visual processes than does the ARE and involves spatial working memory.

Shape-assimilation effect: retrospective distortion of visual shapes

A brief visual stimulus distorts the perceived shape of a subsequent visual stimulus as being dissimilar to the shape of a previous stimulus (shape-contrast effect). In this study, we presented a visual stimulus after a to-be-estimated target stimulus and found that the perceived shape of the target stimulus appeared to be similar to the shape of the following stimulus (shape-assimilation effect). The assimilation effect occurred even when the following stimulus was presented at positions different from that of the target stimulus, indicating that the shape-assimilation effect is a nonretinotopic distortion. The results suggest that the preceding and succeeding stimuli differentially modulate the perceived shape of a briefly presented stimulus.

Illusory motion and mislocalization of temporally offset target in apparent motion display

When a visual target briefly appears in a display containing visual motion information, the perceived position of the target is mislocalized forward along its direction of motion. This phenomenon is assumed to be caused by the interaction between the transient onset signal of the target and motion information. However, while transient onset and offset signals are important for the establishment of our perceptual awareness, it has not been examined whether transient offset signals could be also effective for target mislocalization. Here, we demonstrate that shifts in perceived position occurred for a visual target containing a temporally transient offset signal in an apparent motion (AM) display. First, with horizontal AM, we found that illusory motion was perceived when a static target transiently and repeatedly blinked at a fixed position. The perceived direction of the illusory motion was in counter-phase with that of the AM stimuli. Further, we confirmed that illusory motion was frequently perceived when (1) the eccentricity of the target was larger, (2) offset duration was longer, and (3) smoother AM was perceived. Illusory motion was not perceived unless AM stimuli were presented after the offset signal, while illusory motion still occurred when the AM stimuli disappeared before the offset signal. In addition, we found that mislocalization of the target’s perceived position actually occurred in a direction opposite to AM. These findings suggest that a transient offset signal could trigger perceptual mislocalization of static visual stimuli by interacting with motion information in a postdictive manner.

Depth modulation of the attentional repulsion effect

Shifts of attention can cause mislocalisation of visual objects. Abriefcue that attracts attention can cause a shift in the perceived location of a subsequently presented visual object--specifically, moving it away from the focus of attention (attentional repulsion). In the present study we investigated whether depth would influence the magnitude of attentional repulsion by presenting peripheral visual cues in different depth planes from the target or fixation. In experiment 1 the results showed that the magnitude of the attentional repulsion was larger when the cue was presented at the depth plane farther away from the target and fixation. In experiment 2 we presented the fixation point in the same depth plane as the nearest cues and found larger repulsion effects when the cues were presented in depth planes farther away from the fixation. In experiment 3 no depth modulation was observed when the fixation was presented in the same depth plane with the farthest cues. Taken together, when the cues were presented in the depth plane farther away from the fixation, the magnitude of the attentional repulsion effect increased. It is speculated that the residual coarser spatial representation in the space farther from the fixation plane or the enhanced attentional process for the space closer than the fixation may be responsible for the larger attentional repulsion effect.

Smaller holistic processing of faces associated with face drawing experience

The type of experience involved with an object category has been regarded as one important factor in shaping of the human object recognition system. Laboratory training studies have shown that different kinds of learning experience with the same set of novel objects resulted in different perceptual and neural changes. Whether this applies to natural real-world objects remains to be seen. We compared two groups of observers who had different learning experiences with faces, using holistic processing as a dependent measure. We found that, while ordinary observers had extensive individuation experience with faces and displayed typical holistic face processing, art students who had acquired additional experience in drawing faces, and thus in attending to parts of a face, showed less holistic processing than did ordinary observers. These results converge with laboratory training studies on the role of type of experience in the development of different perceptual markers for different object categories. It is thus insufficient to categorize expertise simply in terms of object domains (e.g., expertise with faces). Instead, perceptual expertise should be classified in terms of the underlying process or task demand.

Mislocalization of visual stimuli: independent effects of static and dynamic attention

Shifts of visual attention cause systematic distortions of the perceived locations of visual objects around the focus of attention. In the attention repulsion effect, the perceived location of a visual target is shifted away from an attention-attracting cue when the cue is presented before the target. Recently it has been found that, if the visual cue is presented after the target, the perceived location of the target shifts toward the location of the following cue. One unanswered question is whether a single mechanism underlies both attentional repulsion and attraction effects. We presented participants with two disks at diagonal locations as visual cues and two vertical lines as targets. Participants were asked to perform a forced-choice task to judge targets' positions. The present study examined whether the magnitude of the repulsion effect and the attraction effect would differ (Experiment 1), whether the two effects would interact (Experiment 2), and whether the location or the dynamic shift of attentional focus would determine the distortions effects (Experiment 3). The results showed that the effect size of the attraction effect was slightly larger than the repulsion effect and the preceding and following cues have independent influences on the perceived positions. The repulsion effect was caused by the location of attnetion and the attraction effect was due to the dynamic shift of attentional focus, suggesting that the underlying mechanisms for the retrospective attraction effect might be different from those for the repulsion effect.