The attentional requirements of consciousness

It has been widely claimed that attention and awareness are doubly dissociable and that there is no causal relation between them. In support of this view are numerous claims of attention without awareness, and awareness without attention. Although there is evidence that attention can operate on or be drawn to unconscious stimuli, various recent findings demonstrate that there is no empirical support for awareness without attention. To properly test for awareness without attention, we propose that a stimulus be studied using a battery of tests based on diverse, mainstream paradigms from the current attention literature. When this type of analysis is performed, the evidence is fully consistent with a model in which attention is necessary, but not sufficient, for awareness.     

Familiarity does not affect the unilateral field advantage for repetition detection

We have previously reported evidence that repetitions of letters, colors, sizes, and common motion paths are more rapidly detected when they are presented unilaterally (i.e., both in the same visual field) versus bilaterally (one element in each visual field; Butcher and Cavanagh (Attention, Perception, & Psychophysics 70:714?C724, 2008). Here, we report evidence that this unilateral field advantage (UFA) for repetition detection does not depend on prior experience with the elements that comprise the repetition. In Experiment 1, native English, Persian, and Japanese speakers were tested on a repetition detection task involving characters from Western, Arabic, and Japanese character sets. The character sets were tested in blocks, in each of which subjects were presented with four characters for 16 ms and asked to report whether any two of the characters were identical. The subjects were faster detecting repetitions that were presented unilaterally rather than bilaterally, and there was no interaction with stimulus familiarity. A second experiment replicated this finding with native English speakers only, using a longer stimulus duration (150 ms). We had previously proposed that the UFA arises because the low-level processes that group physically identical items operate more efficiently within than across hemifields. Our data now indicate that this grouping process is insensitive to item familiarity, supporting the claim that the process is low-level.     

Attentional sampling of multiple wagon wheels

Attending to a periodic motion stimulus can induce illusory reversals of the direction of motion. This continuous wagon wheel illusion (c-WWI) has been taken to reflect discrete sampling of motion information by visual attention. An alternative view is that it is caused by adaptation. Here, we attempt to discriminate between these two interpretations by asking participants to attend to multiple periodic motion stimuli: The discrete attentional sampling account, but not the adaptation account, predicts a decrease of c-WWI temporal-frequency tuning with set size (with a single periodic motion stimulus the c-WWI is tuned to a temporal frequency of 10 Hz). We presented one to four rotating gratings that occasionally reversed direction while participants counted reversals. We considered reversal overestimations as manifestations of the c-WWI and determined the temporal-frequency tuning of the illusion for each set size. Optimal temporal frequency decreased with increasing set size. This outcome favors the discrete attentional sampling interpretation of the c-WWI, with a sampling rate for each individual stimulus dependent on the number of stimuli attended.     

The influence of cast shadows on visual search

We show that cast shadows can have a significant influence on the speed of visual search. In particular, we find that search based on the shape of a region is affected when the region is darker than the background and corresponds to a shadow formed by lighting from above. Results support the proposal that an early-level system rapidly identifies regions as shadows and then discounts them, making their shapes more difficult to access. Several constraints used by this system are mapped out, including constraints on the luminance and texture of the shadow region, and on the nature of the item casting the shadow. Among other things, this system is found to distinguish between line elements (items containing only edges) and surface elements (items containing visible surfaces), with only the latter deemed capable of casting a shadow.     

The use of stimulus dimensions in judgement making in spider fearful and nonfearful individuals

This study uses a multidimensional scaling approach to investigate the hypothesis that spider fearful individuals give priority to a threat-safety dimension when making judgments. The results show that when making judgments about stimuli, spider fearful individuals (1) placed significantly greater comparative weighting on a threat-relevant dimension than on a non-emotive dimension (colour), and (2) tended to rate threatening pairs of stimuli and safe pairs of stimuli as more similar than did the nonfearful group. This prioritised dimensional processing suggests a mechanism by which phobics can exhibit what initially appear to be paradoxical tendencies to give priority to both threat and safety information.     

Calibration of peripheral perception of shape with and without saccadic eye movements

The cortical representations of a visual object differ radically across saccades. Several studies claim that the visual system adapts the peripheral percept to better match the subsequent foveal view. Recently, Herwig, Weiß, and Schneider (2015, Annals of the New York Academy of Sciences, 1339(1), 97–105) found that the perception of shape demonstrates a saccade-dependent learning effect. Here, we ask whether this learning actually requires saccades. We replicated Herwig et al.’s (2015) study and introduced a fixation condition. In a learning phase, participants were exposed to objects whose shape systematically changed during a saccade, or during a displacement from peripheral to foveal vision (without a saccade). In a subsequent test, objects were perceived as less (more) curved if they previously changed from more circular (triangular) in the periphery to more triangular (circular) in the fovea. Importantly, this pattern was seen both with and without saccades. We then tested whether a variable delay between the presentations of the peripheral and foveal objects would affect their association—hypothetically weakening it at longer delays. Again, we found that shape judgments depended on the changes experienced during the learning phase and that they were similar in both the saccade and fixation conditions. Surprisingly, they were not affected by the delay between the peripheral and foveal presentations over the range we tested. These results suggest that a general associative process, independent of saccade execution, contributes to the perception of shape across viewpoints.

     

Surrounding motion affects the perceived locations of moving stimuli

The perceived position of an object is determined not only by the retinal location of the object but also by gaze direction, eye movements, and the motion of the object itself. Recent evidence further suggests that the motion of one object can alter the perceived positions of stationary objects in remote regions of visual space (Whitney & Cavanagh, 2000). This indicates that there is an influence of motion on perceived position, and that this influence can extend over large areas of the visual field. Yet, it remains unclear whether the motion of one object shifts the perceived positions of other moving stimuli. To test this we measured two well-known visual illusions, the Fröhlich effect and representational momentum, in the presence of extraneous surrounding motion. We found that the magnitude of these mislocalizations was altered depending on the direction and speed of the surrounding motion. The results indicate that the positions assigned to stationary and moving objects are affected by motion signals over large areas of space and that both types of stimuli may be assigned positions by a common mechanism.