Spatial asymmetries in viewing and remembering scenes: consequences of an attentional bias?

Fixating picture boundaries does not eliminate boundary extension: implications for scene representation

Observers frequently remember seeing more of a scene than was shown (boundary extension). Does this reflect a lack of eye fixations to the boundary region? Single-object photographs were presented for 14-15 s each. Main objects were either whole or slightly cropped by one boundary, creating a salient marker of boundary placement. All participants expected a memory test, but only half were informed that boundary memory would be tested. Participants in both conditions made multiple fixations to the boundary region and the cropped region during study. Demonstrating the importance of these regions, test-informed participants fixated them sooner, longer, and more frequently. Boundary ratings (Experiment 1) and border adjustment tasks (Experiments 2-4) revealed boundary extension in both conditions. The error was reduced, but not eliminated, in the test-informed condition. Surprisingly, test knowledge and multiple fixations to the salient cropped region, during study and at test, were insufficient to overcome boundary extension on the cropped side. Results are discussed within a traditional visual-centric framework versus a multisource model of scene perception.

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.

Leftward biases in picture scanning and line bisection: a gaze-contingent window study

A bias for humans to attend to the left side of space has been reported in a variety of experiments. While patients with hemispatial neglect mistakenly bisect horizontal lines to the right of centre, neurologically healthy individuals show a mean leftward error. Here, two experiments demonstrated a robust tendency for participants to saccade to the left when viewing photographs. We were able to manipulate this bias by using an asymmetrical gaze-contingent window, which revealed more of the scene on one side of fixation-causing participants to saccade more often in that direction. A second experiment demonstrated the same change in eye movements occurring rapidly from trial to trial, and investigated whether it would carry over and effect attention during a line bisection task. There was some carry-over from gaze-contingent scene viewing to the eye movements during line bisection. However, despite frequent initial eye movements and many errors to the left, manual responses were not affected by this change in orienting. We conclude that the mechanisms underlying asymmetrical attention in picture scanning and line bisection are flexible and can be separated, with saccades in scene perception driven more by a skewed perceptual span.

Visual and memory search in complex environments: determinants of eye movements and search performance

Previous research on visual and memory search revealed various top down and bottom up factors influencing performance. However, utilising abstract stimuli (e.g. geometrical shapes or letters) and focussing on individual factors has often limited the applicability of research findings. Two experiments were designed to analyse which attributes of a product facilitate search in an applied environment. Participants scanned displays containing juice packages while their eye movements were recorded. The familiarity, saliency, and position of search targets were systematically varied. Experiment 1 involved a visual search task, whereas Experiment 2 focussed on memory search. The results showed that bottom up (target saliency) and top down (target familiarity) factors strongly interacted. Overt visual attention was influenced by cultural habits, purposes, and current task demands. The results provide a solid database for assessing the impact and interplay of fundamental top down and bottom up determinants of search processes in applied fields of psychology. Practitioner Summary: Our study demonstrates how a product (or a visual item in general) needs to be designed and placed to ensure that it can be found effectively and efficiently within complex environments. Corresponding product design should result in faster and more accurate visual and memory based search processes.

Vertical representational biases in healthy university students

In line bisection tasks neurologically intact individuals tend to bisect lines slightly left of their midpoint for horizontal lines, and above centre for vertical lines, a phenomenon known as perceptual pseudoneglect (Bowers & Heilman, 1980; Van Vugt, Fransen, Creten, & Paquiner, 2000). Recent investigations have demonstrated the leftward bias to extend to mental imagery, a finding known as representational pseudoneglect (McGeorge, Beschin, Colnaghi, Rusconi, & Della Sala, 2007). This paper examined whether the upward bias found in perceptual tasks extended to mental imagery in healthy individuals. University students studied a diagram depicting a central character and target objects that were located in six positions relative to the person in the diagram (left/right, up/down, and front/back). Following learning, participants recalled the locations of the objects from several imagined orientations. Performance on the recall task revealed faster response latencies for upward targets, providing evidence for vertical representational biases in healthy individuals.

Saccade control in natural images is shaped by the information visible at fixation: evidence from asymmetric gaze-contingent windows

When people view images, their saccades are predominantly horizontal and show a positively skewed distribution of amplitudes. How are these patterns affected by the information close to fixation and the features in the periphery? We recorded saccades while observers encoded a set of scenes with a gaze-contingent window at fixation: Features inside a rectangular (Experiment 1) or elliptical (Experiment 2) window were intact; peripheral background was masked completely or blurred. When the window was asymmetric, with more information preserved either horizontally or vertically, saccades tended to follow the information within the window, rather than exploring unseen regions, which runs counter to the idea that saccades function to maximize information gain on each fixation. Window shape also affected fixation and amplitude distributions, but horizontal windows had less of an impact. The findings suggest that saccades follow the features currently being processed and that normal vision samples these features from a horizontally elongated region.

Hemifield asymmetry in the potency of exogenous auditory and visual cues

Neurologically normal subjects misperceive the midpoints of lines (PSE) as reliably leftward of veridical center, a phenomenon known as pseudoneglect. This leftward bias reflects the dominance of the right cerebral hemisphere in deploying spatial attention. Transient visual cues, delivered to either the left or right endpoints of lines, modulate PSE such that leftward biases are increased by leftward cues, and are decreased by rightward cues, relative to a no-cue control condition. We ask whether lateralized auditory cues can similarly influence PSE in a tachistoscopic visual line bisection task, and describe how visual and auditory cues, in spatially synergistic or antagonistic combinations, jointly influence PSE. Our results demonstrate that whereas auditory and visual cues both modulate PSE, visual cues are overall more potent than auditory cues. Visual and auditory cues are weighted such that visual cues are significantly more potent than auditory cues when visual cues are delivered to left hemispace. Visual and auditory cues are equipotent when visual cues are delivered to right hemispace. These results are consistent with the existence of independent lateralized networks governing the deployment of visuospatial and audiospatial attention. An analysis of the weighting of unisensory visual and auditory cues which optimally predicts PSE in multisensory cue conditions shows that cues combine additively. There was no evidence for a superadditive multisensory cue combination.

Biases of spatial attention in vision and audition

Neurologically normal observers misperceive the midpoint of horizontal lines as systematically leftward of veridical center, a phenomenon known as pseudoneglect. Pseudoneglect is attributed to a tonic asymmetry of visuospatial attention favoring left hemispace. Whereas visuospatial attention is biased toward left hemispace, some evidence suggests that audiospatial attention may possess a right hemispatial bias. If spatial attention is supramodal, then the leftward bias observed in visual line bisection should also be expressed in auditory bisection tasks. If spatial attention is modality specific then bisection errors in visual and auditory spatial judgments are potentially dissociable. Subjects performed a bisection task for spatial intervals defined by auditory stimuli, as well as a tachistoscopic visual line bisection task. Subjects showed a significant leftward bias in the visual line bisection task and a significant rightward bias in the auditory interval bisection task. Performance across both tasks was, however, significantly positively correlated. These results imply the existence of both modality specific and supramodal attentional mechanisms where visuospatial attention has a prepotent leftward vector and audiospatial attention has a prepotent rightward vector of attention. In addition, the biases of both visuospatial and audiospatial attention are correlated.

Boundary extension: findings and theories

A view of a scene is often remembered as containing information that might have been present just beyond the actual boundaries of that view, and this is referred to as boundary extension. Characteristics of the view (e.g., scene or nonscene; close-up or wide-angle; whether objects are cropped, static, or in motion, emotionally neutral or emotionally charged), display (e.g., aperture shape and size; target duration; retention interval; whether probes of memory involve magnification/minification or change in physical distance), and observer (e.g., allocation of attention; age; planned fixation, gaze direction, and eye movements; monocular or binocular viewing; prior exposure; neurological correlates) that influence boundary extension are reviewed. Proposed mechanisms of boundary extension (perceptual, memory, or motion schema; extension-normalization; attentional selection; errors in source monitoring) are discussed, and possible relationships of boundary extension to other cognitive processes (e.g., representational momentum; remembered distance and remembered size; amodal completion; transsaccadic memory) are briefly addressed.