Perception

When the right eye and the left eye view dissimilar scenes, the observer does not experience a stable superimposed percept of the images presented to the two eyes, but instead perceives an alternation between the images seen by each eye. A critical question confronting this robust and intriguing phenomenon of binocular rivalry is how the visual system selects the image to be perceived (dominant). The current main-stream literature emphasizes a bottom – up explanation in which the rivalry stimulus with the higher contour strength has the advantage, and becomes dominant in rivalry. Nevertheless, some workers in the past have favored an attention-selection explanation for binocular rivalry. We investigated the role of attention in binocular rivalry by employing novel psychophysical paradigms which capitalized on several established phenomena (eg the Cheshire Cat effect, attention cueing, pop-out effect). Our results revealed two major aspects of attention modulation in binocular rivalry. We found that a dominant image is less likely to be suppressed when voluntary attention is directed to it. This suggests the role of voluntary attention in retaining the dominant image in visual awareness. Second, a rivalry stimulus is more likely to become dominant if accompanied by a pop-out cue (in the same eye and proximity). Since a pop-out cue attracts involuntary attention to its location/eye, this result suggests that cue-mediated involuntary attention can promote the ability of a rivalry stimulus to reach visual awareness.

We investigated preferred or canonical views for familiar and three-dimensional nonsense objects using computer-graphics psychophysics. We assessed the canonical views for objects by allowing participants to actively rotate realistically shaded three-dimensional models in realtime. Objects were viewed on a Silicon Graphics workstation and manipulated in virtual space with a three-degree-of-freedom input device. In the first experiment, participants adjusted each object to the viewpoint from which they would take a photograph if they planned to use the object to illustrate a brochure. In the second experiment, participants mentally imaged each object on the basis of the name and then adjusted the object to the viewpoint from which they imagined it. In both experiments, there was a large degree of consistency across participants in terms of the preferred view for a given object. Our results provide new insights on the geometrical, experiential, and functional attributes that determine canonical views under ecological conditions.

When we look at an object as we move or the object moves, our visual system is presented with a sequence of different views of the object. It has been suggested that such regular temporal sequences of views of objects contain information that can aid in the process of representing and recognising objects. We examined whether seeing a series of perspective views of objects in sequence led to more efficient recognition than seeing the same views of objects but presented in a random order. Participants studied images of 20 novel three-dimensional objects rotating in depth under one of two study conditions. In one study condition, participants viewed an ordered sequence of views of objects that was assumed to mimic important aspects of how we normally encounter objects. In the other study condition, participants were presented the same object views, but in a random order. It was expected that studying a regular sequence of views would lead to more efficient recognition than studying a random presentation of object views. Although subsequent recognition accuracy was equal for the two groups, differences in reaction time between the two study groups resulted. Specifically, the random study group responded reliably faster than the sequence study group. Some possible encoding differences between the two groups are discussed.

Circularly repeating patches containing sawtooth luminance gradients produce a sensation of motion when viewed in the periphery. Illusory motion is perceived in a dark-to-light direction, but only when one's gaze is directed to different locations around the stimulus, a point outside the display is fixated and the observer blinks, or when the stimulus is sequentially displayed at different locations whilst the observer fixates one point. We propose that the illusion is produced by the interaction of three factors: (i) introducing transients as a result of eye movements or blinks; (ii) differing latencies in the processing of luminance; and (iii) spatiotemporal integration of the differing luminance signals in the periphery.

A 120-frame movie, which can be downloaded from specified web sites, allows an observer to see the qualitative form of his or her temporal modulation transfer function. Results collected from two of the authors are presented.

Two experiments were conducted to explore Gillam and Borsting's (1988, Perception 17 603–608) report that uncorrelated monocular texture facilitates stereopsis by shortening the latency to see depth in random-dot stereograms. Experiment 1 used stereograms similar, in pattern but not disparity, to Gillam and Borsting's with monocular texture present or absent. A third condition, where monocular texture was dissimilar to the binocular panels and background, was also used. We were unable to generalize the findings of Gillam and Borsting for a depth step of 6 min of arc to a larger depth step of 24 min of arc. That is, we observed no significant difference in latencies between the conditions with monocular texture absent and present at a disparity of 24 min of arc. We found latencies to be significantly longer in the monocular-texture-different condition than the monocular-texture-absent condition, however. We account for this, ad hoc, by arguing that the monocular-texture-different stereogram depicts a rare or ‘accidental’ visual scenario. This account was supported by the results of experiment 2 which showed that stereograms depicting accidental views yielded longer latencies than those depicting generic views. We conclude that the ecological validity of monocular texture must also be considered when assessing the effects of monocular texture on stereopsis.

In four studies children were asked to read aloud a passage of randomly ordered common words with and without a coloured sheet of plastic (overlay) placed upon the page. The children's rate of reading increased with the overlay, for some children more than for others. The children were also asked to undertake a test of texture segmentation in which targets consisting of a structured texture had to be distinguished from within a random background texture. The texture segmentation was improved when the overlay was used, again for some children more than for others. The improvement in texture segmentation was, in general, correlated with the improvement in rate of reading. Slower readers were generally poorer at texture segmentation. The implications for reading, for texture segmentation, and for clinical tests of vision are discussed.

L, a 47-year-old female of Choctaw descent, was first identified as a potential synaesthete on the basis of self-report data regarding digit-colour associations. Upon completion of the identification procedures typified in the literature, it was concluded that L met the classic memory-performance criteria used to identify synaesthetic ability. A series of Stroop-type tasks were then performed to identify the dynamics of her synaesthetic experiences. The results of these analyses provided three findings of note. First, the clear pattern of response-time differences between L and the control group suggests that tasks designed to produce involuntary divisions of attention can be an effective means by which to demonstrate that synaesthetic experiences are involuntary but elicited. Second, the significantly slower performance by L on a negative-priming Stroop list shaped around her colour – digit associations indicates the presence of a lexical component in her synaesthetic experience. Third, the use of a manual colour-classification task for which a verbal response was not employed served to confirm the presence of a lexical component in L's synaesthetic experiences. The implications of these results for current synaesthetic theories are then discussed. Finally, a clustering solution of a portion of L's colour–digit experiences is presented, along with the ramifications of its results on the nature of L's perceptual experience.