Perception

Our visual representation of facial expression is examined in this study: is this representation built from edge information, or does it incorporate surface-based information? To answer this question, photographic negation of grey-scale images is used. Negation preserves edge information whilst disrupting the surface-based information. In two experiments visual aftereffects produced by prolonged viewing of images of facial expressions were measured. This adaptation-based technique allows a behavioural assessment of the characteristics encoded by the neural systems underlying our representation of facial expression. The experiments show that photographic negation of the adapting images results in a profound decrease of expression aftereffect. Our visual representation of facial expression therefore appears to not just be built from edge information, but to also incorporate surface information. The latter allows an appreciation of the 3-D structure of the expressing face that, it is argued, may underpin the subtlety and range of our non-verbal facial communication.

Although gaze direction and face shape have each been shown to affect perceptions of the dominance of others, the question whether gaze direction and face shape have independent main effects on perceptions of dominance, and whether these effects interact, has not yet been studied. To investigate this issue, we compared dominance ratings of faces with masculinised shapes and direct gaze, masculinised shapes and averted gaze, feminised shapes and direct gaze, and feminised shapes and averted gaze. While faces with direct gaze were generally rated as more dominant than those with averted gaze, this effect of gaze direction was greater when judging faces with masculinised shapes than when judging faces with feminised shapes. Additionally, faces with masculinised shapes were rated as more dominant than those with feminised shapes when faces were presented with direct gaze, but not when faces were presented with averted gaze. Collectively, these findings reveal an interaction between the effects of gaze direction and sexually dimorphic facial cues on judgments of the dominance of others, presenting novel evidence for the existence of complex integrative processes that underpin social perception of faces. Integrating information from face shape and gaze cues may increase the efficiency with which we perceive the dominance of others.

What are the uncurved lines in our visual field? To answer this question, Helmholtz developed a geometrical model of line-curvature perception, and demonstrated it with his famous checkerboard pattern with pin-cushion distortion. He claimed it looked perfectly regular when viewed monocularly at close range while fixating the centre. Recently, doubts have been expressed whether this demonstration actually works. We tested twenty monocular, stationary observers who could adjust the distortion of a checkerboard pattern over a large range, from barrel-shaped to pin-cushion-shaped. Their task was to adjust the curvature of the edges of the checks such that the checkerboard looked straight and regular. In one condition they had to fixate the centre of the pattern, in another condition they were instructed to let their gaze wander. We found that most observers indeed perceived a pattern with pin-cushion distortion as undeformed, thereby seeing hyperbolic curves in the figure as uncurved lines in the visual field. They set a more strongly curved pattern in the fixation condition than in the free-viewing condition, as also described by Helmholtz. Interestingly, the effect is about half as strong as Helmholtz claimed. Furthermore, we found considerable inter-individual differences.

Helmholtz's famous distorted chessboard pattern has been used to make the point that perception of the straightness of peripherally viewed lines is not always veridical. Helmholtz showed that the curved lines of his chessboard pattern appear to be straight when viewed from a critical distance and he argued that, at this distance, the contours stimulated particular ‘direction circles’ in the field of fixation. We measured the magnitude of the distortion of peripherally viewed contours, and found that the straightness of elongated contours is indeed misperceived in the direction reported by Helmholtz, but that the magnitude of the effect varies with viewing conditions. On the basis of theoretical considerations, we conclude that there cannot, in principle, be particular retinal loci (‘loci’ is used here in the sense of an arc or an extended set of points that provide a basis for judging collinearity) to underpin our judgments of the straightness and parallelity of peripheral contours, because such judgments also require information about the 3-D surface upon which the contours are located. Moreover, we show experimentally that the contours in the real world that are judged to be straight and parallel can stimulate quite different retinal loci, depending on the shape of the 3-D surface upon which they are drawn.

The aim of the present study was to investigate how perceptual binding and selective attention operate during infants' and adults' visual search of an illusory figure. An eye-tracker system was used to test adults and infants in two conditions: illusory and non-illusory (real). In the illusory condition, a Kanizsa triangle was embedded among distractor pacmen which did not generate illusory contours. In the non-illusory condition, a real triangle was included in the same pacmen's display. The results showed that adults detected both the Kanizsa and the real figure automatically and without focal attention (experiment 1). In contrast, 6-month-old infants showed a pop-out effect only for the real figure (experiment 2). The failure of the illusory figure to trigger infants' attention was not due to infants' inability to perceive the illusory figure per se, as infants preferred the illusory figure over a non-illusory control stimulus in a classical preferential-looking task (experiment 3). Overall, these findings indicate that the illusory Kanizsa triangle triggers visual attention in adults, but not in infants, supporting evidence that at 6 months of age the binding processes involved in the perception of a Kanizsa figure do not operate in an adult-like manner.

Perception relates not only to the optical information from the environment but also to the perceiver's performance on a given task. We present evidence that the perceived height and width of an American-football field goal post relates to the perceiver's kicking performance. Participants who made more successful kicks perceived the field goal posts to be farther apart and perceived the crossbar to be closer to the ground compared with participants who made fewer kicks. Interestingly, the current results show perceptual effects related to performance only after kicking the football but not before kicking. We also found that the types of performance errors influenced specific aspects of perception. The more kicks that were missed left or right of the target, the narrower the field goal posts looked. The more kicks that were missed short of the target, the taller the field goal crossbar looked. These results demonstrate that performance is a factor in size perception.

Previous work has demonstrated that providing a verbal description of a wine impairs its recognition (Melcher and Schooler, 1996 Journal of Memory and Language 35 231–245). It was proposed that the effect was due to disruption of the perceptual memory by the verbalisation process as seen in face recognition. A similar impairment can be observed in face recognition after reading the small (local) letters of Navon stimuli. Here, it is suggested that the effect in wine recognition is due to a change in the processing style following the provision of a verbal description. In the current experiment we investigated whether the reading of Navon letters also affected the recognition of wines. We found that wine recognition was more accurate after the reading of the global letters rather than after the reading of the local letters of the Navon stimuli. The results demonstrate how the control of visual processing can affect perception in other modalities.

A single experiment was carried out to evaluate the ability of younger and older observers to discriminate object weights. A 2-alternative forced-choice variant of the method of constant stimuli was used to obtain difference thresholds for lifted weight for twelve younger (mean age = 21.5 years) and twelve older (mean age = 71.3 years) adults. The standard weight was 100 g, whereas the test weights ranged from 85 to 115 g. The difference thresholds of the older observers were 57.6% higher than those of the younger observers: the average difference thresholds were 10.4% and 6.6% of the standard for the older and younger observers, respectively. The current findings of an age-related deterioration in the ability to discriminate lifted weight extend and disambiguate the results of earlier research.

Two experiments were carried out to examine the effects of dominant right versus non-dominant left exploration hand and left versus right object orientation on haptic recognition of familiar objects. In experiment 1, participants named 48 familiar objects in two blocks. There was no dominant-hand advantage to naming objects haptically and there was no interaction between exploration hand and object orientation. Furthermore, priming of naming was not reduced by changes of either object orientation or exploration hand. To test whether these results were attributable to a failure to encode object orientation and exploration hand, experiment 2 replicated experiment 1 except that the unexpected task in the second block was to decide whether either exploration hand or object orientation had changed relative to the initial naming block. Performance on both tasks was above chance, demonstrating that this information had been encoded into long-term haptic representations following the initial block of naming. Thus when identifying familiar objects, the haptic processing system can achieve object constancy efficiently across hand changes and object-orientation changes, although this information is often stored even when it is task-irrelevant.

In this study, I examined how sequential stream segregation contributes to the detection of diotic tones among tones with time-varying interaural time differences (ITDs). Target (T) and distractor (D) tones, and a silent duration (–) formed a sequence (DTD–) and this sequence was presented repeatedly. A frequency difference was introduced between target and distractor tones. The distractor tones were also given time-varying ITDs to produce a percept of smooth auditory motion along the interaural axis. In half of the trials, the target tones were not given time-varying ITDs, and thus were diotically presented. The task of the listeners was to determine whether the repeated sequences of DTD–had target tones without motion. The sensitivity d′ for the detection of diotic target tones was higher with larger frequency differences. On the other hand, the criterion c was lower with larger frequency differences. In another session, I confirmed that proportions of reports “two streams” was positively and negatively correlated with d′ and c, respectively. The results indicate that the localisation of a sound image could be influenced by sequential stream segregation in complex sound environments.

We carried out two experiments to test the relationship between real-time perception of structural change in stylistically unusual musical sounds, and perception of its affect (arousal and valence). Computer music was used because of its unfamiliarity and our capacity to control it in ecologically appropriate ways. In experiment 1, thirteen participants unselected for musical training participated in tasks to detect segmentation and changes in affect. Changes in affect occurred upon detection of segmentation; but not all algorithmically distinct segments conveyed distinct affect. Short segments followed by long segments led to greater changes in arousal and valence at the point of segmentation than vice versa. In experiment 2, intra-segment sound transitions were introduced. Sixteen musicians performed the same affect task as in experiment 1, and a novel change in sound task. Participants were slow to respond to a continuous transition, but quick to respond to instantaneous transitions. Contrary to literature on the perception of affect in more familiar music, the musician participants in experiment 2 differed more in their ratings of arousal than of valence, in spite of a strong correlation of arousal with the composition of the stimuli. These findings are discussed in relation to the positive valence attributed to the more familiar sounds in both experiments.

When oblique rows of black and white dots drifted horizontally across a mid-grey surround, the perceived direction of motion was shifted to be almost parallel to the dotted lines and was often nearly orthogonal to the real motion. The reason is that the black/white contrast signals between adjacent dots along the length of the line are stronger than black/grey or white/grey contrast signals across the line, and the motion is computed as a vector sum of local contrast-weighted motion signals.

We investigated amodal completion with changes in two parameters: figure orientation, and the shape of the occluding and occluded figures. First, Markovich's [2002, Visual Mathematics 4(1); http://www.mi.sanu.ac.rs/vismath/fila] figure was presented in vertical, horizontal, and diagonal orientations. The results supported Markovich's finding of amodal completion by smooth continuity and symmetry. Amodal completion was also affected by orientation: symmetrical shape tended to appear when the pattern had vertical axis whilst smooth continuity appeared in diagonal orientation. Next, the shape of the exposed side of the occluded figure was changed from straight to curved. Finally, the shape of the grey occluder was changed from a disk to a half-disk or a quarter-disk. The results then showed the influence of the visible contour on amodal completion. This shows that the contextual relation of the whole figure is significant in amodal completion.

Hammad et al (2008, Perception 37 504–510) argue that the apparent shape of a drawn ellipse in the context of a drawn cylinder is mediated by the presence of local ‘depth cues’. I attempt to show that such features are incapable of constraining the shape of the whole pattern—and thus of its parts—in the manner claimed by the authors, and offer alternative explanations for their experimental outcome.