Selective adaptation of monocular and binocular neurons in human vision

Psychophysical techniques were used to examine how subpopulations of visual neurons varying in their ocular dominance interacted in determining performance on a visual task. Using an asymmetric alternating adaptation of the left and right eyes, we manipulated the sensitivity of monocularly driven neurons while keeping the sensitivity of binocularly driven neurons constant. Relative threshold elevations were measured in the left eye, right eye, and both eyes of five observers following different ratios of alternating adaptation. It was found that whereas monocularly measured aftereffects varied monotonically as a function of the adaptation duration of the measured eye, the magnitude of the binocularly measured aftereffect remained constant regardless of how the adaptation was divided between the two eyes. This suggests that neurons differing in their ocular dominance pool their activity in determining sensitivity to a test target.     

Autokinetic movement and inverted vision

It was considered that inverted vision could influence the condition of the subject's relative framework. The aim of this study was to investigate whether autokinetic movement observed during inverted vision might differ from that in normal vision. One subject wearing inverting spectacles and another one subject in normal vision observed autokinetic movement for five days. The results showed that directional changes increased with the time spent in visual inversion, while in normal vision such tendency was not observed. One speculative interpretation was suggested in terms of subject-related framework.     

Fragmentation of monocular afterimages in individuals with and without normal binocular vision

Monocular afterimages of a vertical line were generated in each eye of binocularly normal individuals and of those lacking binocular single vision or stereopsis as a consequence of childhood strabismus. Fragmentations and disappearances of the afterimages occurred less frequently in the strabismic than in the normal subjects; they were also less frequent in the dominant (nonamblyopic) eyes of the strabismics than in their amblyopic eyes. The afterimages remained visible for longer when presented to the dominant eyes of the strabismic subjects, and a similar effect was found between the sighting dominant and nondominant eyes of normal subjects.     

Three- to eight-month-old infants' catching under monocular and binocular vision

We report a cross-sectional and a longitudinal experiment that examined developmental changes in the relative contribution of monocular and binocular variables in the guidance of interceptive arm movements. Three- to eight-month-old infants were observed while presented with differently sized balls that approached frontally with a constant velocity under both monocular and binocular viewing conditions. Movement onset indicated that with age infants increasingly came to rely on binocular variables in controlling the timing of the interceptive arm movements. That is, from 7 to 8 months of age movement onset was independent from object size under binocular but not under monocular viewing. In contrast, binocular viewing enhanced the spatial accuracy of the interceptive arm movements at all ages. We concluded that attunement to binocular information is a key process in infants' gaining adaptive control of goal-directed arm movements. However, interceptive arm movements entail the formation of multiple on-line couplings between optic and movement variables, each of which appears to develop at its own pace.     

Monocular and binocular vision in the control of goal-directed movement

In the present research the authors examined the time course of binocular integration in goal-directed aiming and grasping. With liquid-crystal goggles, the authors manipulated vision independently to the right and left eyes of 10 students during movement preparation and movement execution. Contrary to earlier findings reported in catching experiments (I. Olivier, D. J. Weeks, K. L. Ricker, J. Lyons, & D. Elliott, 1998), neither a temporal nor a spatial binocular advantage was obtained in 1 grasping and 2 aiming studies. That result suggests that, at least in some circumstances, monocular vision is sufficient for the precise control of limb movements. In a final aiming experiment involving 3-dimensional spatial variability and no trial-to-trial visual feedback about performance, binocular vision was associated with greater spatial accuracy. Binocular superiority appeared to be most pronounced when participants were unable to adjust their limb control strategy or procedure on the basis of terminal feedback about performance.     

Interaction of vision and movement via a mirror

I have noticed a striking effect that vision can have on movement: when a person makes circular motions with both hands, clockwise with the left hand, counterclockwise with the right hand, while watching the reflection of one hand in a parasagitally placed mirror, if one arm makes a vertical excursion, the other arm tends to make the same vertical excursion, but not typically if the excursing arm is viewed in plain vision. This observation may help in understanding how visual feedback via a mirror may be beneficial for rehabilitation of some patients with movement deficits secondary to certain neurologic conditions, and illustrates that the traditional division of neural processes into sensory input and motor output is somewhat arbitrary.     

Apparent movement detection in the pigeon

Pigeons were trained to discriminate between the presence and absence of apparent movement in visual displays. Generalization gradients obtained on the dimension of speed indicated a broad range of movement detection. Extremely accurate discrimination performance on displays varying in direction of movement suggested formation of a "movement concept".     

Binocular and monocular detection of Gabor patches in binocular two-dimensional noise

Contrast thresholds for detecting sine-wave Gabor patches in two-dimensional externally added random-pixel noise were measured. Thresholds were obtained for monocular and binocular signals in the presence of spatial correlated (identical) and uncorrelated (independent) noise in the two eyes. Measurements were obtained at four different spectral densities of noise (including zero). Thresholds were higher for monocular stimuli than for binocular, and higher in the presence of correlated noise compared to uncorrelated noise. The magnitude of binocular summation, similar in correlated and uncorrelated noise, decreased with increasing noise strength. The independent contributions of internal noise and sampling efficiency to detection were analysed. Sampling efficiencies were higher for binocular than for monocular viewing for both types of noise, with values being higher with uncorrelated noise. Binocular stimuli showed a lower equivalent noise level compared to the mean monocular case for both types of noise.     

The contribution of peripheral and central vision in the control of movement amplitude

Past research has revealed that central vision is more important than peripheral vision in controlling the amplitude of target-directed aiming movements. However, the extent to which central vision contributes to movement planning versus online control is unclear. Since participants usually fixate the target very early in the limb trajectory, the limb enters the central visual field during the late stages of movement. Hence, there may be insufficient time for central vision to be processed online to correct errors during movement execution. Instead, information from central vision may be processed offline and utilised as a form of knowledge of results, enhancing the programming of subsequent trials. In the present research, variability in limb trajectories was analysed to determine the extent to which peripheral and central vision is used to detect and correct errors during movement execution. Participants performed manual aiming movements of 450 ms under four different visual conditions: full vision, peripheral vision, central vision, no vision. The results revealed that participants utilised visual information from both the central and peripheral visual fields to adjust limb trajectories during movement execution. However, visual information from the central visual field was used more effectively to correct errors online compared to visual information from the peripheral visual field.     

Detectability of motion as a factor in depth perception by monocular movement parallax

A display of two objects at different distances was presented to 10 observers, who were requested in two experiments to match the width of the more distant (comparison) object to the width of the nearer (standard) one under conditions permitting monocular observation and lateral head motion. The matched width of the comparison object was considered a measure of the effectiveness of movement parallax. The effectiveness of movement parallax decreases with increasing angular separation of the objects and with increasing background distance. A background without visible texture leads to a better perception of depth between two objects than a textured background The results can be explained by postulating that, whenever the detectability of motion is enhanced, i.e., the threshold for the detection of motion is lowered, the effectiveness of movement parallax as a cue to depth is increased.     

Exploring the limits of peripheral vision for the control of movement

The role played by peripheral visual information in the control of aiming movements is not fully understood, as is indicated by the conflicting results reported in the literature. In the present study, the authors tested and confirmed the hypothesis that the source of the conflict lies in the portion of the visual peripheral field that has been under scrutiny in the different studies. Participants (N = 60) moved a computer mouse from a fixed starting position to 1 of 3 targets under varied vision conditions. The portion of the peripheral visual field that best ensured directional accuracy of a sweeping movement was found to be located between 20 degrees and 10 degrees of visual angle, whereas the area found to favor directional accuracy of an aiming movement comprised 30 degrees through 10 degrees of visual angle.     

Effects of midbrain central gray lesions on spontaneous and electrically induced aggression in the rat

Large electrolytic lesions were placed in the midbrain central gray of male rats. Their effects on hypothalamically induced aggression, switch-off behaviour, and locomotion were investigated. A number of these animals were also tested for territorial intermale aggression in order to compare electrically induced and spontaneous aggression. Large lesions resulted in an increase of the current threshold to induce aggression by hypo-thalamic stimulation. Smaller, but still quite large, lesions decreased the threshold current for hypothalamic aggression. After the operation a decrease in the threshold for switch-off was present, both in the experimental and the control group. Current thresholds for locomotion were decreased after the lesions only in the experimental group. Spontaneous aggression was temporarily decreased after the lesion. No indication was found that other behavioural elements of the animal were distorted by the lesion. The parallel between the effects on spontaneous and electrically induced aggression makes it attractive to ascribe a role to the neural circuit of hypothalamus and central gray in territorial aggression. However, even with large lesions the animals were still capable of fighting, hence the central gray is not indispensable. An attempt was made to explain the differential effects that differently sized central gray lesions have on hypothalamic aggression.     

Effects of fornix transection on spontaneous and trained non-matching by monkeys

Three monkeys with fornix transection and three normal control monkeys performed a series of tasks which were variations of delayed non-matching. Experiment 1 showed that even at short retention intervals fornix transection impaired the spontaneous tendency to explore novel objects. Experiment 2 provided differential reward for non-matching and showed that the fornix-transected monkeys learned and performed non-matching normally even though the sample-match retention intervals were long throughout the experiment. Experiment 3 showed that non-matching performance was transiently more disrupted in fornix-transected than in normal monkeys when the testing procedure was changed, in a variety of ways, while maintaining the basic non-match rule. Experiment 4 required the monkeys to discriminate objects they had displaced from objects they had seen but not displaced; fornix transection produced in this task a substantial and stable impairment. These four experiments require a revised interpretation of the effects of fornix transection upon recognition memory and exploration. Particularly they contradict the hypothesis, suggested by previous experiments, that fornix transection produces a defect in discrimination of stimulus familiarity in long-term but not in short-term memory. They suggest rather that fornix transection impairs memory of instrumental responses.     

The dynamic programming matching analysis of handwriting movement in delayed vision

Abstract: Dynamic programming matching analysis of the velocity profile of handwriting was used to examine temporally invariant characteristics of handwriting. This was done by comparing the performance of 12 subjects in writing five words under various delayed visual feedback conditions. The rate of temporally invariant handwriting decreased when delay of visual feedback was introduced. That is, the mean number of fluctuations or hesitations increased as a function of the delay time. This indicates that subjects wrote words by segmenting their movements into submovements. The relative positions of the boundaries of submovements was shown using dynamic programming matching analysis by the distribution of fluctuations along a time axis of templates. The results suggest the development of a segmented "move-and-wait" strategy under conditions of delayed vision. It was shown that in the "move" phase, subjects performed appropriate submovements as smoothly as in the no delay condition and waited during the delay until visual feedback caught up. The increased errors were due to inadequate segmentation of movements.