Perception

The perceived motion direction of a moving Glass pattern is influenced by the orientation of the dot pairs (dipoles) that generate the pattern (Krekelberg et al, 2003 Nature 424 674–677; Ross, 2004 Vision Research 44 441–448). Here, we investigate how the motion vector and the dipole orientation of moving Glass patterns influence the perceived orientation of each. We employed 1 s movie presentations of sequences of linear Glass patterns, each consisting of 200 dot pairs. Signal pairs, aligned in a common orientation, moved in a common direction. The observer's task was to indicate either the perceived direction of motion, or the perceived dipole orientation of Glass patterns that consisted of either same-polarity dipoles, or opposite-polarity dipoles. Perceived orientation or motion direction was measured as a function of the angular difference between the orientation and the motion direction of the dipoles. We found that the apparent global direction of motion was attracted by approximately 4° towards the dipole orientation for small (15°, 23°) angular differences between dipole motion-direction and dipole orientation, regardless of dipole polarity. However, under the same stimulus conditions, the apparent global orientation was much less affected by the direction of motion, suggesting that motion and form interact asymmetrically. Global form influences global motion-direction perception more powerfully than global motion influences global form perception.

When locomoting in a physically challenging environment, the body draws upon available energy reserves to accommodate increased metabolic demand. Ingested glucose supplements the body's energy resources, whereas non-caloric sweetener does not. Two experiments demonstrate that participants who had consumed a glucose-containing drink perceived the slant of a hill to be less steep than did participants who had consumed a drink containing non-caloric sweetener. The glucose manipulation influenced participants' explicit awareness of hill slant but, as predicted, it did not affect a visually guided action of orienting a tilting palmboard to be parallel to the hill. Measured individual differences in factors related to bioenergetic state, such as fatigue, sleep quality, fitness, mood, and stress, also affected perception: lower energetic states were associated with steeper perceptions of hill slant. This research shows that the perception of the spatial layout of the environment is influenced by the energetic resources available for locomotion within it. Our findings are consistent with the view that spatial perceptions are influenced by bioenergetic factors.

Research suggests that blind people are superior to sighted in echolocation, but systematic psychoacoustic studies on environmental conditions such as distance to objects, signal duration, and reverberation are lacking. Therefore, two experiments were conducted. Noise bursts of 5, 50, or 500 ms were reproduced by a loudspeaker on an artificial manikin in an ordinary room and in an anechoic chamber. The manikin recorded the sounds binaurally in the presence and absence of a reflecting 1.5-mm thick aluminium disk, 0.5 m in diameter, placed in front, at distances of 0.5 to 5 m. These recordings were later presented to ten visually handicapped and ten sighted people, 30–62 years old, using a 2AFC paradigm with feedback. The task was to detect which of two sounds that contained the reflecting object. The blind performed better than the sighted participants. All performed well with the object at < 2 m distance. Detection increased with longer signal durations. Performance was slightly better in the ordinary room than in the anechoic chamber. A supplementary experiment on the two best blind persons showed that their superior performance at distances > 2 m was not by chance. Detection thresholds showed that blind participants could detect the object at longer distances in the conference room than in the anechoic chamber, when using the longer-duration sounds and also as compared to the sighted people. Audiometric tests suggest that equal hearing in both ears is important for echolocation. Possible echolocation mechanisms are discussed.

Face recognition is thought to rely more on the relative positions of face features (configural information) than on the appearance of the individual face parts (featural information). It also seems to rely on a specific band of spatial frequencies (SFs). In this study, we measured the SFs needed for processing configural and featural information using the method of constant stimuli in combination with a simultaneous-matching paradigm. Stimuli were two-octave-wide bandpass-filtered upright and inverted faces that contained either featural or configural modifications. SF thresholds for featural and configural processing were calculated by interpolating between discrimination accuracy scores. Low-pass and high-pass thresholds for featural and configural processing in upright faces were approximately equal, whereas for inverted faces, the thresholds were closer to the middle of the spectrum for configural processing relative to featural processing. Thus, a broader band of SFs, one that overlapped more with the middle of the frequency spectrum, was needed for configural processing than for featural processing in inverted faces. Our findings emphasise the importance of a narrow mid-range band of frequencies for both configural and featural encoding in upright faces and suggest that configural information is extracted less effectively in inverted faces.

Using a composite-face paradigm, we show that social judgments from faces rely on holistic processing. Participants judged facial halves more positively when aligned with trustworthy than with untrustworthy halves, despite instructions to ignore the aligned parts (experiment 1). This effect was substantially reduced when the faces were inverted (experiments 2 and 3) and when the halves were misaligned (experiment 3). In all three experiments, judgments were affected to a larger extent by the to-be-attended than the to-be-ignored halves, suggesting that there is partial control of holistic processing. However, after rapid exposures to faces (33 to 100 ms), judgments of trustworthy and untrustworthy halves aligned with incongruent halves were indistinguishable (experiment 4a). Differences emerged with exposures longer than 100 ms. In contrast, when participants were not instructed to attend to specific facial parts, these differences did not emerge (experiment 4b). These findings suggest that the initial pass of information is holistic and that additional time allows participants to partially ignore the task-irrelevant context.

Clear differences in perceptual and neural processing of faces of different species have been reported, implying the contribution of visual experience to face perception. Can these differences be revealed by our eye scanning patterns while we extract salient facial information? Here, we systematically compared non-pet-owners' gaze patterns while exploring human, monkey, dog, and cat faces in a passive viewing task. Our analysis revealed that the faces of different species induced similar patterns of fixation distribution between left and right hemiface, and among key local facial features, with the eyes attracting the highest proportion of fixations and viewing times, followed by the nose, and then the mouth. Only the proportion of fixations directed at the mouth region was species-dependent and could be differentiated at the earliest stage of face viewing. Our spontaneous eye-scanning patterns associated with face exploration appear to have been mainly constrained by general facial configurations; the species affiliation of the inspected faces had limited impact on gaze allocation, at least under free-viewing conditions.

We investigated the effects of dynamic information on decoding facial expressions. A dynamic face entailed a change from a neutral to a full-blown expression, whereas a static face included only the full-blown expression. Sixty-eight participants were divided into two groups, the dynamic condition and the static condition. The facial stimuli expressed eight kinds of emotions (excited, happy, calm, sleepy, sad, angry, fearful, and surprised) according to a dimensional perspective. Participants evaluated each facial stimulus using two methods, the Affect Grid (Russell et al, 1989 Personality and Social Psychology 29 497–510) and the forced-choice task, allowing for dimensional and categorical judgment interpretations. For activation ratings in dimensional judgments, the results indicated that dynamic calm faces, low-activation expressions were rated as less activated than static faces. For categorical judgments, dynamic excited, happy, and fearful faces, which are high- and middle-activation expressions, had higher ratings than did those under the static condition. These results suggest that the beneficial effect of dynamic information depends on the emotional properties of facial expressions.

All people share implicit mappings across the senses, which give us preferences for certain sensory combinations over others (eg light colours are preferentially paired with higher-pitch sounds; Ward et al, 2006 Cortex 42 264–280). Although previous work has tended to focus on the cross-modality of vision with other senses, here we present evidence of systematic cross-modality between taste and sound. We created four sound continua representing to varying extents phonetic qualities of speech (F1, F2, voice discontinuity, and spectral balance). Sixty-five participants selected their preferred sound to accompany each of the basic tastes of sweet, sour, bitter, and salty, at two different concentrations. We found significant shared preferences among our participants to map certain acoustic qualities to certain types of tastes (eg sweet tastes tend to be mapped to a lower spectral balance than sour tastes). We also found a preference for mapping certain sound qualities to different taste concentrations. Together our data provide the first detailed analysis of how phonetic features map systematically to different tastants and concentrations. We examine the roots of these mappings, and discuss how such associations might guide the ways in which human languages are used to name objects with taste.

We discovered an interesting perceptual distortion in our office where an upright lamp in front of a bookshelf was noticeably curved to form several subtle S-shaped bends. We realized that the books in the bookshelf fell in a particular manner, leaning in alternative directions, which caused the straight lamp to appear bent, creating what may be a real-world example of the Zöllner illusion. Evidence for the production of the illusion diagrammatically and an explanation for the effect are provided.

We report a new illusion in which the edges of diamonds placed at the intersections of grids are perceived to be jaggy (the jaggy diamonds illusion). Interestingly, the illusion disappears when the stimulus is rotated by 45°, when the stimuli are observed at a close distance, and on the diamond at which the observers stare. Luminance contrast between diamonds, grids, and background is a strong determinant for this illusion.