Blind subjects construct conscious mental images of visual scenes encoded in musical form.

Blind (previously sighted) subjects are able to analyse, describe and graphically represent a number of high-contrast visual images translated into musical form de novo. We presented musical transforms of a random assortment of photographic images of objects and urban scenes to such subjects, a few of which depicted architectural and other landmarks that may be useful in navigating a route to a particular destination. Our blind subjects were able to use the sound representation to construct a conscious mental image that was revealed by their ability to depict a visual target by drawing it. We noted the similarity between the way the visual system integrates information from successive fixations to form a representation that is stable across eye movements and the way a succession of image frames (encoded in sound) which depict different portions of the image are integrated to form a seamless mental image. Finally, we discuss the profound resemblance between the way a professional musician carries out a structural analysis of a musical composition in order to relate its structure to the perception of musical form and the strategies used by our blind subjects in isolating structural features that collectively reveal the identity of visual form.     

Portraits and perception: configural information in creating and recognizing face images

Configural information has long been considered important for face recognition. However, traditional portraiture instruction encourages the artist to use a 'generic' configuration for faces rather than attempting to replicate precise feature positions. We examine this intriguing paradox with two tasks designed to test the extent to which configural information is incorporated into face representations. In Experiment 1, we use a simplified face production task to examine how accurately feature configuration can be incorporated in the generated likenesses. In Experiment 2, we ask if the 'portraits' created in Experiment 1 are discriminable from veridical images. The production and recognition results from these experiments show a consistent pattern. Subjects are quite poor at arranging facial features (eyes, nose and mouth) in their correct locations, and at distinguishing erroneous configurations from correct ones. This seeming insensitivity to configural relations is consistent with artists' practice of creating portraits based on a generic geometric template. Interestingly, the frame of reference artists implicitly use for this generic template - the external face contour - emerges as a significant modulator of performance in our experimental results. Production errors are reduced and recognition performance is enhanced in the presence of outer contours. We discuss the implications of these results for face recognition models, as well as some possible perceptual reasons why portraits are so difficult to create.     

The directional flow of visual information transfer between pedestrians

Close behavioural coupling of visual orientation may provide a range of adaptive benefits to social species. In order to investigate the natural properties of gaze-following between pedestrians, we displayed an attractive stimulus in a frequently trafficked corridor within which a hidden camera was placed to detect directed gaze from passers-by. The presence of visual cues towards the stimulus by nearby pedestrians increased the probability of passers-by looking as well. In contrast to cueing paradigms used for laboratory research, however, we found that individuals were more responsive to changes in the visual orientation of those walking in the same direction in front of them (i.e. viewing head direction from behind). In fact, visual attention towards the stimulus diminished when oncoming pedestrians had previously looked. Information was therefore transferred more effectively behind, rather than in front of, gaze cues. Further analyses show that neither crowding nor group interactions were driving these effects, suggesting that, within natural settings gaze-following is strongly mediated by social interaction and facilitates acquisition of environmentally relevant information.     

The human visual system is optimised for processing the spatial information in natural visual images

A fundamental tenet of visual science is that the detailed properties of visual systems are not capricious accidents, but are closely matched by evolution and neonatal experience to the environments and lifestyles in which those visual systems must work. This has been shown most convincingly for fish and insects. For mammalian vision, however, this tenet is based more upon theoretical arguments than upon direct observations. Here, we describe experiments that require human observers to discriminate between pictures of slightly different faces or objects. These are produced by a morphing technique that allows small, quantifiable changes to be made in the stimulus images. The independent variable is designed to give increasing deviation from natural visual scenes, and is a measure of the Fourier composition of the image (its second-order statistics). Performance in these tests was best when the pictures had natural second-order spatial statistics, and degraded when the images were made less natural. Furthermore, performance can be explained with a simple model of contrast coding, based upon the properties of simple cells in the mammalian visual cortex. The findings thus provide direct empirical support for the notion that human spatial vision is optimised to the second-order statistics of the optical environment.     

Corticothalamic interactions in the transfer of visual information

Thalamic function does not stand apart, as a discrete processing step, from the cortical circuitry. The thalamus receives extensive feedback from the cortex and this influences the firing pattern, synchronization and sensory response mode of relay cells. A crucial question concerns the extent to which the feedback simply controls the state and transmission mode of relay cells and the extent to which the feedback participates in the specific processing of sensory information. Using examples from experiments examining the influence of feedback from the visual cortex to the lateral geniculate nucleus (LGN), we argue that thalamic mechanisms are selectively focused by visually driven feedback to optimize the thalamic contribution to segmentation and global integration. This involves effects on both the temporal and spatial parameters characterizing the responses of LGN cells and includes, for example, motion-driven feedback effects from MT (middle temporal visual area) relayed via layer 6 of V1 (primary visual cortex).     

The nature and perception of fluctuations in human musical rhythms

Although human musical performances represent one of the most valuable achievements of mankind, the best musicians perform imperfectly. Musical rhythms are not entirely accurate and thus inevitably deviate from the ideal beat pattern. Nevertheless, computer generated perfect beat patterns are frequently devalued by listeners due to a perceived lack of human touch. Professional audio editing software therefore offers a humanizing feature which artificially generates rhythmic fluctuations. However, the built-in humanizing units are essentially random number generators producing only simple uncorrelated fluctuations. Here, for the first time, we establish long-range fluctuations as an inevitable natural companion of both simple and complex human rhythmic performances. Moreover, we demonstrate that listeners strongly prefer long-range correlated fluctuations in musical rhythms. Thus, the favorable fluctuation type for humanizing interbeat intervals coincides with the one generically inherent in human musical performances.     

The role of information transfer under different food patterns: a simulation study

The aim of this paper is to address the question of how informationtransfer affects foraging efficiency in a colonial breedingsituation. By creating computer simulations, we attempt to modelinformation transfer of food location by individuals withinthe colony. Three kinds of foraging strategy were modeled: searcher–noinformation transfer (solo foraging), watcher–limitedinformation transfer (local enhancement), and a mixture of watcherand follower–full information transfer (information center).The predictability of food was changed by varying patchiness(ratio of food patches) and duration of food patches. When thefood occurs in many randomly distributed patches and the fooddensity in each is low, the solitary searcher strategy givesthe best foraging efficiency. The significance of informationtransfer strategies and colonial breeding on foraging efficiencyincrease when food becomes more clumped. The solitary watcherstrategy is the best at intermediately clumped food distribution.Colonial breeding gives the best foraging efficiency when theinformation center operates and there are some high-densityfood patches.     

The physics of visual perception

By measuring the contrast threshold for gratings of different waveform and spatial frequency, Campbell & Robson suggested in 1968 that there may be 'channels' tuned to different spatial frequencies. By using the technique of adapting to a high contrast grating, it was possible to measure the band-pass characteristics of these channels. Similar techniques were used to establish the orientational tuning of the channels. Reasons are put forward why it is advantageous to organize the visual system in this manner.     

The perception of visual motion.

Recent developments have led to a greater insight into the complex processes of perception of visual motion. A better understanding of the neuronal circuitry involved and advances in electrophysiological techniques have allowed researchers to alter the perception of an animal with a stimulating electrode. In addition, studies have further elucidated the processes by which signals are combined and compared, allowing a greater understanding of the effects of selective brain damage.     

Propagation of photon noise and information transfer in visual motion detection

The extraction of the direction of motion from the time varying retinal images is one of the most basic tasks any visual system is confronted with. However, retinal images are severely corrupted by photon noise, in particular at low light levels, thus limiting the performance of motion detection mechanisms of what sort so ever. Here, we study how photon noise propagates through an array of Reichardt-type motion detectors that are commonly believed to underlie fly motion vision. We provide closed-form analytical expressions of the signal and noise spectra at the output of such a motion detector array. We find that Reichardt detectors reveal favorable noise suppression in the frequency range where most of the signal power resides. Most notably, due to inherent adaptive properties, the transmitted information about stimulus velocity remains nearly constant over a large range of velocity entropies. Action editor: Matthew Wiener     

The neural basis of visual body perception

The human body, like the human face, is a rich source of socially relevant information about other individuals. Evidence from studies of both humans and non-human primates points to focal regions of the higher-level visual cortex that are specialized for the visual perception of the body. These body-selective regions, which can be dissociated from regions involved in face perception, have been implicated in the perception of the self and the 'body schema', the perception of others' emotions and the understanding of actions.     

Form perception and visual acuity in a chimpanzee

A 6.5-year-old female chimpanzee learned to distinguish perfectly every letter of the alphabet in a matching-to-sample task with 26 letters as choice alternatives. Confusion of letters during the initial training was used to scale them in a multidimensional similarity space and to associate them in hierarchical clusters. The results resembled those obtained from similarity judgements by humans. Using letters of various sizes, a visual acuity test revealed that the chimpanzee's acuity was about 1.5, comparable to that in normal humans. The chimpanzee also readily learned to use letters as names of individual humans and chimpanzees. A species-typical feature was identified in the perceptual processes associated with complex forms, such as those involved in individual recognition.