Perception

Dodge, in 1916, suggested that the French term ‘saccade’ should be used for describing the rapid movements of the eyes that occur while reading. Previously he had referred to these as type I movements. Javal had used the term ‘saccade’ in 1879, when describing experiments conducted in his laboratory by Lamare. Accordingly, Javal has been rightly credited with assigning the term to rapid eye movements. In English these rapid rotations had been called jerks, and they had been observed and measured before Lamare's studies of reading. Rapid sweeps of the eyes occur as one phase of nystagmus; they were observed by Wells in 1792 who used an afterimage technique, and they were illustrated by Crum Brown in 1878. Afterimages were used in nineteenth-century research on eye movements and eye position; they were also employed by Hering in 1879, to ascertain how the eyes moved during reading. In the previous year, Javal had employed afterimages in his investigations of reading, but this was to demonstrate that the eyes moved horizontally rather than vertically. Hering's and Lamare's auditory method established the discontinuous nature of eye movements during reading, and the photographic methods introduced by Dodge and others in the early twentieth century enabled their characteristics to be determined with greater accuracy.

Our ability to recognise the usual horizontal orientation of our own face (mirror orientation) as compared with another very familiar face (normal orientation) was examined in experiment 1. Participants did not use the same kind of information in determining the orientation of their own face as in determining the orientation of the other familiar face. The proportion of participants who reported having based their judgment on the location of an asymmetric feature (eg a mole) was higher when determining the orientation of their own face than when determining that of the other familiar face. In experiment 2, participants were presented with pairs of manipulated images of their own face and of another familiar face showing conflicting asymmetric features and configural information. Each pair consisted of one picture showing asymmetric features of a given face in a mirror-reversed position, while the facial configuration was left unchanged; and one picture in which the location of the asymmetric features was left unchanged, while the facial configuration was mirror-reversed. As expected from the hypothesis that asymmetric local features are more frequently used for the judgment of one's own face, participants chose the picture showing mirror-reversed asymmetric features when determining the usual orientation of their own face significantly more often than they chose the picture showing normally oriented asymmetric features when determining the orientation of the other face. These results are explained in terms of competing forward and mirror-reversed representations of one's own face.

We examined how the recognition of facial emotion was influenced by manipulation of both spatial and temporal properties of 3-D point-light displays of facial motion. We started with the measurement of 3-D position of multiple locations on the face during posed expressions of anger, happiness, sadness, and surprise, and then manipulated the spatial and temporal properties of the measurements to obtain new versions of the movements. In two experiments, we examined recognition of these original and modified facial expressions: in experiment 1, we manipulated the spatial properties of the facial movement, and in experiment 2 we manipulated the temporal properties. The results of experiment 1 showed that exaggeration of facial expressions relative to a fixed neutral expression resulted in enhanced ratings of the intensity of that emotion. The results of experiment 2 showed that changing the duration of an expression had a small effect on ratings of emotional intensity, with a trend for expressions with shorter durations to have lower ratings of intensity. The results are discussed within the context of theories of encoding as related to caricature and emotion.

In the leading model of face perception, facial identity and facial expressions of emotion are recognized by separate mechanisms. In this report, we provide evidence supporting the independence of these processes by documenting an individual with severely impaired recognition of facial identity yet normal recognition of facial expressions of emotion. NM, a 40-year-old prosopagnosic, showed severely impaired performance on five of six tests of facial identity recognition. In contrast, she performed in the normal range on four different tests of emotion recognition. Because the tests of identity recognition and emotion recognition assessed her abilities in a variety of ways, these results provide solid support for models in which identity recognition and emotion recognition are performed by separate processes.

Subjects observed and reproduced abstract, irregular stimulus models generated by the steady movement of a disk across two-dimensional paths. The paths comprised 3 to 7 randomly oriented linear segments linked head-to-foot. Reproductions were expressed by moving a stylus over the surface of a graphics tablet while the disk was tracing its trajectory (concurrent reproduction), or soon after the disk had finished (delayed reproduction). For both concurrent and delayed conditions, fidelity of reproduction fell with increasing number of segments in the model. Overall quality of reproduction did not differ between the two conditions. When a few models were repeated, interspersed among non-repeated ones, performance improved but only when reproduction was delayed. This improvement was stimulus-selective, not a general improvement with practice. Two additional experiments showed that (i) memory for a seen model is well preserved for at least 6 s, with relatively modest need for rehearsal, and (ii) successful reproduction is possible with remarkably little information having been extracted from key points in the model's trajectory.

It is well established that motion aftereffects (MAEs) can show interocular transfer (IOT); that is, motion adaptation in one eye can give a MAE in the other eye. Different quantification methods and different test stimuli have been shown to give different IOT magnitudes, varying from no to almost full IOT. In this study, we examine to what extent IOT of the dynamic MAE (dMAE), that is the MAE seen with a dynamic noise test pattern, varies with velocity of the adaptation stimulus. We measured strength of dMAE by a nulling method. The aftereffect induced by adaptation to a moving random-pixel array was compensated (nulled), during a brief dynamic test period, by the same kind of motion stimulus of variable luminance signal-to-noise ratio (LSNR). The LSNR nulling value was determined in a Quest-staircase procedure. We found that velocity has a strong effect on the magnitude of IOT for the dMAE. For increasing speeds from 1.5 deg s⁻¹ to 24 deg s⁻¹ average IOT values increased about linearly from 18% to 63% or from 32% to 83%, depending on IOT definition. The finding that dMAEs transfer to an increasing extent as speed increases, suggests that binocular cells play a more dominant role at higher speeds.

Observers in this study judged which of two fields contained the greater number of spots. Spots had difference-of-Gaussian luminance profiles and could differ in contrast polarity or were of uniform luminance and could differ in size. Weber fractions for all observers except one varied little except when spots varied in size. It is suggested that the results of this and previous studies might be explained by the existence of neurons tuned for number.

The planar Euclidean version of the travelling salesperson problem (TSP) requires finding a tour of minimal length through a two-dimensional set of nodes. Despite the computational intractability of the TSP, people can produce rapid, near-optimal solutions to visually presented versions of such problems. To explain this, MacGregor et al (1999, Perception 28 1417–1428) have suggested that people use a global-to-local process, based on a perceptual tendency to organise stimuli into convex figures. We review the evidence for this idea and propose an alternative, local-to-global hypothesis, based on the detection of least distances between the nodes in an array. We present the results of an experiment in which we examined the relationships between three objective measures and performance measures of optimality and response uncertainty in tasks requiring participants to construct a closed tour or an open path. The data are not well accounted for by a process based on the convex hull. In contrast, results are generally consistent with a locally focused process based initially on the detection of nearest-neighbour clusters. Individual differences are interpreted in terms of a hierarchical process of constructing solutions, and the findings are related to a more general analysis of the role of nearest neighbours in the perception of structure and motion.

An investigation of tactile picture perception is reported. Blindfolded sighted subjects explored either ‘line drawings’ or ‘textured’ tactile pictures produced on Zytex swell paper. All pictures were ‘two-dimensional’, that is they depicted only one object face and so did not represent a third dimension. Both picture sets represented the same objects. Results revealed that the textured pictures, in which solid surfaces of depicted objects were uniformly textured, were recognised more often than tactile line drawings, in which surfaces of objects were simply bounded by lines. There were no significant correlations between imagery ability (visual, cutaneous, or kinaesthetic) and picture recognition success. Texture may be a form of ‘uniform connectedness’ (Palmer and Rock 1994 Psychonomic Bulletin & Review 1 29–55) or ‘common region’ (Palmer 1992 Cognitive Psychology 24 436–447), highlighting the global characteristics of stimuli. We argue that textured pictures may encourage the haptic system to take a more globally oriented approach to tactile picture perception, benefiting recognition.