Pseudoneglect in back space

Back and front peripersonal space: behavioural and EMG evidence of top-down and bottom-up mechanisms

Previous studies have identified a 'defensive graded field' in the peripersonal front space where potential threatening stimuli induce stronger blink responses, mainly modulated by top-down mechanisms, which include various factors, such as proximity to the body, stimulus valence, and social cues. However, very little is known about the mechanisms responsible for representation of the back space and the possible role of bottom-up information. By means of acoustic stimuli, we evaluated individuals' representation for front and back space in an ambiguous environment that offered some degree of uncertainty in terms of both distance (close vs. far) and front-back egocentric location of sound sources. We aimed to consider verbal responses about localization of sound sources and EMG data on blink reflex. Results suggested that stimulus distance evaluations were better explained by subjective front-back discrimination, rather than real position. Moreover, blink response data were also better explained by subjective front-back discrimination. Taken together, these findings suggest that the mechanisms that dictate blink response magnitude might also affect sound localization (possible bottom-up mechanism), probably interacting with top-down mechanisms that modulate stimuli location and distance. These findings are interpreted within the defensive peripersonal framework, suggesting a close relationship between bottom-up and top-down mechanisms on spatial representation.

Different audio spatial metric representation around the body

Vision seems to have a pivotal role in developing spatial cognition. A recent approach, based on sensory calibration, has highlighted the role of vision in calibrating hearing in spatial tasks. It was shown that blind individuals have specific impairments during audio spatial bisection tasks. Vision is available only in the frontal space, leading to a "natural" blindness in the back. If vision is important for audio space calibration, then the auditory frontal space should be better represented than the back auditory space. In this study, we investigated this point by comparing frontal and back audio spatial metric representations. We measured precision in the spatial bisection task, for which vision seems to be fundamental to calibrate audition, in twenty-three sighted subjects. Two control tasks, a minimum audible angle and a temporal bisection were employed in order to evaluate auditory precision in the different regions considered. While no differences were observed between frontal and back space in the minimum audible angle (MAA) and temporal bisection task, a significant difference was found in the spatial bisection task, where subjects performed better in the frontal space. Our results are in agreement with the idea that vision is important in developing auditory spatial metric representation in sighted individuals.

In (or outside of) your neck of the woods: laterality in spatial body representation

Beside language, space is to date the most widely recognized lateralized systems. For example, it has been shown that even mental representations of space and the spatial representation of abstract concepts display lateralized characteristics. For the most part, this body of literature describes space as distal or something outside of the observer or actor. What has been strangely absent in the literature on the whole and specifically in the spatial literature until recently is the most proximal space imaginable – the body. In this review, we will summarize three strands of literature showing laterality in body representations. First, evidence of hemispheric asymmetries in body space in health and, second in body space in disease will be examined. Third, studies pointing to differential contributions of the right and left hemisphere to illusory body (space) will be summarized. Together these studies show hemispheric asymmetries to be evident in body representations at the level of simple somatosensory and proprioceptive representations. We propose a novel working hypothesis, whereby neural systems dedicated to processing action-oriented information about one’s own body space may ontogenetically serve as a template for the perception of the external world.

Representational pseudoneglect: a review

Pseudoneglect, the tendency to be biased towards the left-hand side of space, is a robust and consistent behavioural observation best demonstrated on the task of visuospatial line bisection, where participants are asked to centrally bisect visually presented horizontal lines at the perceived centre. A number of studies have revealed that a representational form of pseudoneglect exists, occurring when participants are asked to either mentally represent a stimulus or explore a stimulus using touch in the complete absence of direct visuospatial processing. Despite the growing number of studies that have demonstrated representational pseudoneglect there exists no current and comprehensive review of these findings and no discussion of a theoretical framework into which these findings may fall. An important gap in the current representational pseudoneglect literature is a discussion of the developmental trajectory of the bias. The focus of the current review is to outline studies that have observed representational pseudoneglect in healthy participants, consider a theoretical framework for these observations, and address the impact of lifespan factors such as cognitive ageing on the phenomenon.

Representational pseudoneglect in line bisection

"Representational pseudoneglect" refers to a bias toward the left side of space that occurs when visual information is remembered. Recently a number of demonstrations of such representational pseudoneglect have appeared. In the present article, we report an experiment in which we adopted the classic line bisection paradigm to study representational pseudoneglect. Participants bisected horizontal lines that were shown in extrapersonal space. When the lines were visible on the screen, there was no evidence of any leftward bias. However, when lines were bisected from memory, the participants demonstrated a clear bias to the left. This is the first demonstration of a leftward bias in the bisection of remembered visually presented lines.

Touching base: The effect of participant and stimulus modulation factors on a haptic line bisection task

Acquiring information about our environment through touch is vital in everyday life. Yet very little literature exists about factors that may influence haptic or tactile processing. Recent neuroimaging studies have reported haptic laterality effects that parallel those reported in the visual literature. With the use of a haptic variant of the classical line bisection task, the present study aimed to determine the presence of laterality effects on a behavioural level. Specifically, three handedness groups including strong dextrals, strong sinistrals, and-the to-date largely neglected group of-mixed-handers were examined in their ability to accurately bisect stimuli constructed from corrugated board strips of various lengths. Stimulus factors known to play a role in visuospatial perception including stimulus location, the hand used for bisection, and direction of exploration were systematically varied through pseudo-randomisation. Similar to the visual domain, stimulus location and length as well as participants' handedness and the hand used for bisection exerted a significant influence on participants' estimate of the centre of haptically explored stimuli. However, these effects differed qualitatively from those described for the visual domain, and the factor direction of exploration did not exert any significant effect. This indicates that laterality effects reported on a neural level are sufficiently pronounced to result in measurable behavioural effects. The results, first, add to laterality effects reported for the visual and auditory domain, second, are in line with supramodal spatial processing and third, provide additional evidence to a conceptualisation of pseudoneglect and neglect as signs of hemispheric attentional asymmetries.

Visual processing asymmetries in change detection

Change detection is critically dependent on attentional mechanisms. However, the relation between an asymmetrical distribution of visuo-spatial attention and the detection of changes in visual scenes is not clear. Spatial tasks are known to induce a stronger activation of the right hemisphere. The effects of such visual processing asymmetries induced by a spatial task on change detection were investigated. When required to detect changes in the left and in the right visual fields, participants were significantly faster in detecting changes on the left than on the right. Importantly, this left-side superiority in change detection is not influenced by inspection time, suggesting a critical role of visual processing benefit for the left visual field.

Audiotactile interactions in front and rear space

The last few years have seen a growing interest in the assessment of audiotactile interactions in information processing in peripersonal space. In particular, these studies have focused on investigating peri-hand space [corrected] and, more recently, on the functional differences that have been demonstrated between the space close to front and back of the head (i.e., the peri-head space). In this review, the issue of how audiotactile interactions vary as a function of the region of space in which stimuli are presented (i.e., front vs. rear, peripersonal vs. extra-personal) will be described. We review evidence from both monkey and human studies. This evidence, providing insight into the differential attributes qualifying the frontal and the rear regions of space, sheds light on an until now neglected research topic and may help to contribute to the formulation of new rehabilitative approaches to disorders of spatial representation. A tentative explanation of the evolutionary reasons underlying these particular patterns of results, as well as suggestions for possible future developments, are also provided.

Items on the left are better remembered

Neurologically intact individuals show a spatial processing bias in perception tasks, specifically showing a bias towards the left in bisecting lines. We present evidence for a novel finding that a leftwards bias occurs in short-term memory for recently presented arbitrary bindings of visual features. Three experiments are reported, two of which involve a total of over 60,000 participants with a small number of trials for each. Experiment 3 involved a larger number of trials for each of 144 participants. Participants reproduced from immediate memory arrays of shape–colour–location bindings. In all three experiments, significantly more errors were observed in reproduction of items presented on the right of the array than on the left. Results could not be accounted for by perceptual errors, or by order of presentation or order of reproduction. Findings suggest that items presented on the left are better remembered, indicating a spatial asymmetry in forming or retrieving feature bindings in visual short-term memory.

A lateralized bias in mental imagery: evidence for representational pseudoneglect

One hundred right-handed healthy individuals were asked to imagine a familiar scene (the Piazza del Duomo, Milan) from two opposite viewpoints and report what they could see. For elements that should be visible from the participants' viewpoint, more elements were reported from the left side of the image than from the right, irrespective of view. These results establish that there is a lateralized bias in reporting the details in mental images--representational pseudoneglect. This bias is in the opposite direction and significantly smaller than the bias seen in individuals with representational neglect following right hemisphere damage. Representational pseudoneglect appears analogous to perceptual pseudoneglect and the two may share an underlying mechanism. The results are interpreted as indicating that pseudo-representational neglect arises as the result of a bias in the allocation of attention to the imagined scene.