Perception

Each of a group of one-month-old infants was reinforced, contingent upon nonnutritive sucking, with its mother's voice and the voice of a stranger. In this experiment, two conditions were applied. Under the first, the mother's speech was aimed at communicating with the infant, while, under the second, the mother's speech lacked prosodic and intonational aspects of normal speech. It was shown that infants will suck more for their mother's voices under the intonated condition only. It was concluded that a young infant prefers its own mother's voice provided the mother speaks normally.

While visually fixating on a central, coloured object, thirty-six infants aged between two and five months were presented with a peripheral target to the right or to the left of midline. Both objects were presented at two distances: either 30 or 90 cm from the infant. The extent of the effective visual field was measured by the presence and the latency of saccadic shifts of gaze from the fixation object toward the target object placed at varying degrees of eccentricity. The effective visual field expanded between two and four months. Near peripheral targets were detected at greater angles of eccentricity than those more distant, but this effect was modified both by age and by the distance of central fixation. For two- and three-month infants the effective visual field was most reduced when the central fixation object was placed at 30 cm and the target object at 90 cm. The ability to respond to peripheral objects more distant than the fixation object develops after three months.

Reaching for noise-making objects presented in darkness declines, then recovers, during infancy. The most probable explanation of this U-shaped function would seem to involve changes in reaching, changes in the perception of success, and changes in the body schema. There is no need to postulate any U-shaped change within the auditory system.

Infants with Down's syndrome are delayed in achieving motor milestones. When they first sit unsupported a discrepancy between visual and mechanical-vestibular indices of postural stability is less disruptive of their balance than in normal infants. Yet when they first stand unsupported, the same discrepancy disrupts balance more in these infants than in the normal infants. The effect of discrepant visual feedback also differs systematically as a function of the infants' experience of the posture. Monitoring posture in relation to a stable visual surround appears to be fundamental to the normal development of motor control.

Counterphase gratings, and several other stimuli which consist of equal components of motion in both directions, appeared to drift foveofugally, rather than foveopetally, when presented to the retinal periphery. This ‘foveofugal drift effect’ was demonstrated by descriptive and nulling techniques and its magnitude was shown to vary across subjects. The effect was fairly brief under continuous fixation. Several lines of evidence suggested that eye movements were not responsible for the effect. The phenomenon implies a directional asymmetry in the human visual system which may be related to our consistent exposure to expanding patterns of visual flow.

Contrast thresholds for stereopsis were measured for a variety of bandpass-filtered random-dot stereograms in a series of experiments. The principal finding was that contrast thresholds for stereopsis from ‘complex’ stereograms composed of mixtures of (a) two widely different spatial frequencies or (b) two or more widely different oriented random textures, are considerably lower than would be expected if stereopsis from such stimuli is mediated by the first component to rise above its own stereopsis contrast threshold. Instead, it appears that stereopsis comes about whenever the supradetection-threshold contrast of a stereogram exceeds a certain level, regardless of whether this contrast is provided by a single component or by a mix of two different ones. The implications of these findings for models of stereopsis are discussed.

Astigmatism induced by cylindrical lenses leads to colour sensations similar to the McCollough effect. Consequences for the design of experiments and a new interpretation of the McCollough effect are suggested.

The effect of refractive error was determined for both size constancy and shape constancy. Although an error of 1·5 diopters reduces shape constancy, 3·0 diopters of blur had no effect on size constancy. The results are discussed in terms of the multiple mechanisms subserving the perceptual constancies. The importance of cues from the peripheral visual fields for size constancy and the role of foveally mediated texture and stereopsis cues for shape constancy are emphasized.

Solving problems by imaginal inference often seems inefficient for an organism that is manipulating propositions. One explanation for the apparent inefficiency is that the problems are being solved not in propositional format but by operations in an analogue format. Imaginal inference might then be the most efficient method compatible with the limitations inherent in the analogue format. In the present paper an alternative rationale is given for the use of imaginal inference by explaining how the processes involved in mental problem solving are related to those in perception: it is suggested that the mechanisms used in problem solving have evolved from a perceptual system in which hypotheses about events in the sensory field are generated from an internal representation of the world. This thesis denies that perception is passive and suggests that the capacity for thought is limited by its evolutionary dependence on mechanisms specialized originally for perception. Acceptance of the thesis implies that the capabilities of a propositional format in problem solving would be limited. This limitation could account for the apparently inefficient use of that format in imaginal inference.

Eye movements were recorded while subjects viewed a Kopfermann-like series of Necker cubes and signaled perceptual reversals. At the instant of reversal, subjects tend to fixate the vicinity of the externally appearing corner. These fixations at the instant of reversal tend to have longer duration than those immediately before or after. The longer fixation times associated with perceptual reversal probably reflect the time required to construct the alternate three-dimensional interpretation of the cube. After construction of this new model, the subject then fixates the vicinity of the newly interpreted externally appearing corner.

A geometrical model for computing ‘general perspectives’ is discussed. It is based on the power function r = p(d/t)^1-i, where i is the Thouless index for the phenomenal regression to the real object, r is the real size of the object, p is the apparent size, d is the distance between the subject and the object, and t is the distance between the subject and the projection plane. This model assumes that i is invariant for different distances and this was verified in seventy children and adults at distances of 15 to 120 m. A computer program draws families of curved perspectives which are well-fitted to the actual shape of large visual alleys produced by experiment in open fields.

Three tachistoscopic experiments are reported in which presentation of the target stimulus in a letter/digit categorization task was preceded by a briefly exposed priming stimulus (letter or digit). The primer was subject to backward masking from either the target or a pattern mask, and observers were unaware of its occurrence. With a primer duration of 25 ms, when masking was presumed to be at a central level, performance deteriorated when the two items were from different categories. This inhibition effect was reduced when the characters were physically similar. In contrast, there was little evidence of facilitated processing when primers validly cued targets. At shorter primer durations, when masking is presumed to be peripheral in origin, between-condition differences were less marked. An interpretation in terms of an active model of information processing, with utilization of both categorical and physical information extracted from the primer, is proposed.

A series of lines pointing towards a central region induces an illusory brightness effect that is systematically related to the angle formed by the lines and the contour of the illusory brightness. As the lines veer to become tangents the illusory brightness decreases.