Biomedical subjects

R N Shepard

Publications and source records attributed to R N Shepard.

6 recordsLinked to original sources

PubMed1991

Comparison of cube rotations around axes inclined relative to the environment or to the cube.

Observers judged whether 2 successive computer-displayed rotations of a cube were the same or different. With respect to the observers, each rotation was about a vertical axis (Y), a horizontal (line-of-sight) axis (Z), an axis tilted just 10 degrees from vertical or horizontal, or a maximally oblique axis. Independently, with respect to the cube, each rotation was about a symmetry axis through opposite faces (F) or through opposite corners (C), an axis tilted 10 degrees from one of these symmetry axes, or an axis of extreme nonsymmetry. Speed and accuracy of comparison decreased as the axes of the successive rotations departed from the canonical axes of the environment (Z, or especially, Y), or even more sharply, from the symmetry axes of the cube (C, or especially, F). The internalized principles that guide the perceptual representation of rigid motions evidently are ones of kinematic geometry more than of physics.

Attention↗

PubMed1990

Neural nets for generalization and classification: comment on Staddon and Reid (1990)

The neural net model of Staddon and Reid (1990) explains exponential and Gaussian generalization gradients in the same way as the diffusion model of Shepard (1958). The "cognitive" generalization theory of Shepard (1987), which also has been implemented as a connectionist network, goes beyond both of these models in accounting for classification learning.

Brain↗

PubMed1979

Quantification of the hierarchy of tonal functions within a diatonic context.

Listeners rated test tones falling in the octave range from middle to high C according to how well each completed a diatonic C major scale played in an adjacent octave just before the final test tone. Ratings were well explained in terms of three factors. The factors were distance in pitch height from the context tones, octave equivalence, and the following hierarchy of tonal functions: tonic tone, other tones of the major triad chord, other tones of a diatonic scale, and the nondiatonic tones. In these ratings, pitch height was more prominent for less musical listeners or with less musical (sinusoidal) tones, whereas octave equivalence and the tonal hierarchy prevailed for musical listeners, especially with harmonically richer tones. Ratings for quarter tones interpolated halfway between the halftone steps of the standard chromatic scale were approximately the averages of ratings for adjacent chromatic tones, suggesting failure to discriminate tones at this fine level of division.

Humans↗

PubMed1978

Functional representations common to visual perception and imagination.

Subjects determined whether probe dots appearing in component squares of a 5 X 5 grid fell on a figure that, depending on the condition, was (a) visually presented as a pattern of darkened squares, (b) only remembered from a preceding presentation of such a pattern, or (c) imaginally generated from a verbal code. The speed and accuracy of the responses to the probes as well as the functional dependencies of the reaction times on structural variables were essentially the same whether the figural pattern was imagined, remembered, or actually seen. Reaction times averaged between 400 and 500 msec and were consistently faster (a) for on-figure than for off-figure responses, (b) for simpler figures that had fewer squares, (c) for off-figure probes that were more distant from the figure, and (d) for on-figure probes that consisted either of more dots on the figure or of a dot at the intersection of a horizontal and a vertical bar. The reults were consistent with a model in which a subject's perceptual or imaginal representations of these forms contain barlike units that respond independently to the probes.

Discrimination, Psychological↗

PubMed1976

Perceptual illusion of rotation of three-dimensional objects.

Perspective views of the same three-dimensional object in two orientations, when presented in alternation, produced an illusion of rigid rotation. The minimum cycle duration required for the illusion increased linearly with the angular difference between the orientations and at the same slope for rotations in depth and in the picture plane.

Humans↗

PubMed1975

Mental transformations in the identification of left and right hands.

Subjects determined as rapidly as possible whether each line drawing portrayed a left or a right hand when the drawings were presented in any of four versions (palm or back of either hand) and in any of six orientations in the picture plane. Reaction time varied systematically with orientation and, in the absence of advance information, was over 400 msec longer for the fingers-down orientation. However, when subjects were instructed to imagine a specified (palm or back) view of a specified (left or right) hand in a specified orientation, reaction times to test hands that were consistent with these instructions were short (about 500 msec), independent of orientation, and unacompanied by errors. It is proposed that subjects determine whether a visually presented hand is left or right by moving a mental "phantom" of one of their own hands into the portrayed position and by then comparing its imagined appearance against the appearance of the externally presented hand.

Cues↗