Experienced blind subjects have previously demonstrated good echo perception of size and distance and some echo-discrimination of shapes and textures. In three experiments untrained sighted subjects also proved able to echo-detect and recognize three simple shapes and to recognize fabric and wooden but not carpet and Plexiglas discs at significantly above chance levels. Some improvement occurred over the first few trials but little thereafter, suggesting that this sort of echo perception requires very little training. A blind subject exhibited over-all accuracy comparable to those of sighted subjects. There were, however, interesting differences between the blind subject and the sighted subjects in echo perception of specific stimuli and in approach to the task.

Three experiments with musicians and nonmusicians (N=338) explored variations of Deutsch's musical scale illusion. Conditions under which the illusion occurs were elucidated and data obtained which supported Bregman's suggestion that auditory streaming results from a competition among alternative perceptual organizations. In Experiment 1, a series of studies showed that it is more difficult to induce the scale illusion than might be expected if it is accepted that an illusion will be present for most observers despite minor changes in stimuli and experimental conditions. The stimulus sequence seems better described as an ambiguous figure. Having discovered conditions under which the scale illusion could be reliably induced, Experiments 2 and 3 manipulated additional properties of the stimulus (timbre, loudness, and tune) to provide cues to streaming other than pitch and location. The data showed that streaming of this sequence can be altered by these properties, supporting the notion of a general parsing mechanism which follows general gestalt principles and allows streaming by many stimulus dimensions. Finally, suggestions are made as to how this mechanism might operate.listening to music provides an excellent context for exploring the phenomenon of auditory streaming. Bregman and Campbell (1971) described auditory streaming as the perceptual splitting of concurrent auditory events into separate streams or sequences. This must happen, for example, when listeningto an orchestra. The listener needs to decide which melodies are being played by what instruments, where the sounds originated, and how many instruments and melodies there are.Research on auditory streaming has focused on much simpler situations than listening to an orchestra. Bregman and Campbell, for instance, binaurally presented subjects with a rapid repetitive sequence of six different 100·msec pure tones, three high pitched and three low pitched, one and a half octaves apart. Although successive tones alternated from the high-to low-pitch range, subjects organized the high-and low-pitched sounds into separate auditory streams. Some subjects (59%) claimed that these two streams were successive (i.e., three high tones followed by three low tones, or vice versa); the remainder reported that the streams were concurrent. Neither of these percepts are veridical. Deutsch (1975b) found similar effects when she pre-

It is now held that in conditions where there is conflicting sensory information vision dominates touch. The present study was designed to place boundary conditions on the generality of the hypothesis by comparing the performance of tactually experienced subjects - potters - with university students on a form-perception task in which a square was optically distorted so as to appear rectangular. Subjects examined the square haptically and visually, and matched it by touch or vision. Although potters were more accurate than students when not permitted vision, tactual judgements of both were dominated by vision when they were presented with conflicting information. In a supplementary study longer, more active exploration and emphasis on the necessity of matching by touch had no differential effect. In a third study it was found that a range effect produced by the comparison stimuli could explain the lesser accuracy of the students when they were making haptic judgements. The generality of the hypothesis that vision dominates touch is strengthened by our failure to refute it.

An explanation of apparent direction of rotary motion in depth derived from a general theory of perceptual constancy and illusion is proposed with experimental data in its support. Apparent direction of movement is conceived of as exhibiting perceptual constancy or illusion as a function of apparent direction of orientation in depth for plane objects and apparent relative depth for three-dimensional objects. Apparent reversals of movement direction represent either regular fluctuations between constancy and illusion of direction as a function of valid and invalid stimuli for orientation, or irregular and random fluctuations in their absence. In three preliminary experiments, the apparent movement direction of plane ellipses was investigated as a function of surface pattern information for orientation, and in Experiment I apparent reversals during 20-revolution trials were studied. In Experiment II, apparent movement direction of 3D elliptical V shapes as a function of surface pattern information for relative depth was investigated. In addition to supporting the explanation proposed, the data offer a resolution of a conflict between different theories of apparent reversal of motion in depth.

Wallach has described in qualitative terms the movement of lines behind apertures. We related the data he obtained to the aperture problem, constructed a model of movement perception, and carried out tests of the model. Experiment 1 was a parametric study, and showed the conditions under which a reliable illusion (the barber pole illusion) of diagonal movement of lines along an aperture could be obtained, and when fluctuating judgements or veridical percepts were obtained. On the basis of this study a dipole model was constructed. The model was further developed and tested. In experiment 2 the effects of total area of stimulation were examined: diagonal gratings were viewed behind multiple apertures. In experiment 3 the effects of local signs were examined: diagonal gratings were viewed in an aperture which had edges cut in small steps and stairs, with the risers parallel to the grating, and the treads parallel to the direction of motion of the grating. Experiment 4 was designed to test a prediction about the motion aftereffect of dots near and far from the point of fixation, and the results confirmed the model. It was concluded that the model accounts for the barber pole illusion and, generally, for the movement of gratings in apertures.