Biomedical subjects
Publications and source records attributed to K I Beverley.
Changing-size channels tuned to the oscillation frequency are excited by a stimulus square whose size oscillates at a fixed frequency. In the 0.25-16 Hz frequency band there are at least three kinds of changing-size channels tuned to different frequencies.
Explore the source record for details and available documents.
Psychophysical evidence supports the idea that the human visual pathway computes an object's rate of change of angular size rather independently of the object's trajectory and rather independently of other visual parameters, including contrast and intensity. This independence could provide a basis for accurately judging the component of an object's velocity along a line through the eye in the working visual environment where many visual parameters vary simultaneously. We describe a procedure for quantifying a subject's ability to track changing size, and illustrate the procedure with preliminary experimental data. The subject's R.M.S. tracking errors are displayed in three frequency bands. Our device also measures the perturbing effect of sideways motion upon the subject's ability to track changing size. Such data may go some way to predict a subject's performance in tasks of eye-limb coordination, especially where visual information is largely restricted to the changing-size channel.
Inspecting a radial flow pattern depressed visual sensitivity to changes in the size of a small test square, but only when the square was located near the focus of the flow pattern. The result suggests that precise visual judgments of one's direction of forward motion with respect to the outside world may be mediated by an already known neural organization sensitive to changes in the size of small objects.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
1. Binocular discrimination of the direction of a target's motion in depth was measured in terms of the smallest angular difference in direction that could be detected with a probability 50% better than chance. Directional discrimination was measured for targets moving along 16 different trajectories directed to the left and right of the nose. 2. The relative velocities of the retinal images in the left and right eyes gave a sensitive cue to the direction of the target's motion in depth. 3. The direction of motion was bets discriminated when the target moved along a line directed close to the nose. A change in direction of only 0.2 degrees from this direction of motion could be detected. Discrimination showed two other maxima, one on each side of the central maximum. Discrimination fell to about 0.6-0.8 degrees when the target's direction was changed by only 6 degrees to either side of the nose. 4. The curve of sensitivity to movement in depth had a generally inverse shape to the directional discrimination curve: sensitivity was minimal for trajectories directed near the nose and increased for trajectories directed so as to miss the head. 5. The directional discrimination curve can be related to the sensitivity curves of the four postulated neural mechanisms tuned to different directions of motion in depth; there are three discrimination maxima and, correspondingly, three trajectories for which the slopes of adjacent sensitivity curves differ maximally. This suggests that binocular psychophysical judgements of the direction along which a target moves in depth are to some extent mediated by neural mechanisms that compare (e.g. subtract) the outputs of directionally tuned movement detectors. One function of such neural comparators might be to enhance psychophysical sensitivity to the direction along which a target moves in depth, and thus to provide a physiological basis for precisely judging whether or not an object will hit the head. 6. We suggest that the neural basis for judging the direction of moving objects has an analogy in colour vision where opponent-colour mechanisms enhance sensitivity to wave-length differences in such a way that wave-lengths are more easily discriminated in those parts of the spectrum where the slopes of the pigment action spectra differ maximally.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Viewing a target moving in depth depresses visual sensitivity to depth when test and adapting stimuli simulate motion along closed paths with the same directions of rotation. However, for opposite directions of rotation, sensitivity is either unaffected or increased. This points to two classes of disparity detectors. Either eye's input to a single class of disparity detector consists of the physiological responses to a single direction of horizontal movement.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
1. Visual sensitivity to movement in depth was measured as a function of the relative distances through which the left and right retinal images moved. This relative distance (left:right ratio) provides a sensitive cue to the direction along which a target moves in three-dimensional space.2. Gazing at a target which moved along a fixed direction in space produced a gross reduction of visual sensitivity to movements in depth along that direction. For other directions of movement, visual sensitivity was not affected.3. Sensitivity to depth movement rapidly rose almost to the preadaptation level within the first 20-60 sec after removing the adapting target, but recovery was not complete until 100-300 min had elapsed.4. Any adapting target whose left:right ratio fell within a definite range gave similar reductions of visual sensitivity to movements in depth. There were five such ranges.5. The effects of adapting to movement in depth suggest that eight mechanisms underlie depth perception. These mechanisms are ;tuned' to the direction of movement in three-dimensional space. Four mechanisms are wholly concerned with movements along directions very close to the line which cuts midway between the eyes, and do not respond to movements whose direction departs by more than 1.5 degrees from the preferred direction.6. Neural mechanisms ;tuned' to different left:right ratios could provide a physiological basis for sensing the direction in which an object moves in three-dimensional space.