Spatial Localization Task Research Articles

PREMOTOR CORTEX AND CONDITIONAL MOTOR LEARNING IN MAN

The role of premotor cortex (PMC) in conditional motor learning tasks in man was investigated. Patients with PMC lesions had to learn to associate 6 different visual, tactile or auditory stimuli with 6 different arm movements which were previously rehearsed (Task A). A comparative task involved an association between the same set of sensory stimuli and 6 spatial locations (Task B). Patients with PMC lesions were only impaired when they had to recall a movement from memory on the basis of a sensory cue (Task A), but not for an association involving spatial location (Task B). This indicates that the PMC plays a role in sensory conditional motor learning.

Characteristics of memory impairment following lesioning of the basal forebrain and medial septal nucleus in rats

Memory impairment in rats with lesions of the basal forebrain (BF) and medial septal nucleus (MS) including cell bodies of the cortical and septohippocampal cholinergic systems, respectively, were compared in order to evaluate the functional contribution of the two cholinergic systems to memory. Biochemical assay revealed that lesioning of the BF and MS resulted in marked and selective decreases in both choline acetyltransferase and acetylcholinesterase activities in the cerebral cortex and hippocampus, respectively. Rats with BF lesions exhibited a severe deficit in a passive avoidance task; acquisition of passive avoidance by repeated training was sluggish, and the acquired response was rapidly eliminated in a subsequent extinction test. However, only slight impairment of passive avoidance was observed in rats with MS lesions. Memory impairment in rats with BF or MS lesions was also investigated using two spatial localization tasks, the Morris water task and the 8-arm radial maze task. Both BF and MS lesions elicited a significant impairment in the Morris water task that required reference memory, as demonstrated by an apparent increase in the latency to escape onto a hidden platform in a large water tank. The impairment was much more obvious in the BF-lesioned rats. In contrast, in the radial maze task primarily requiring working memory, rats with lesions of the MS showed severe disruption, exhibiting a marked increase in total errors, a decrease in the number of initial correct responses, and an apparent change in the strategy pattern. However, corresponding changes in the rats with BF lesions were slight. These results suggest that BF lesions may lead to substantial long-term memory impairment while MS lesions may primarily produce short-term or working memory impairm3nt, indicating a qualitatively different contribution of the two cholinergic systems to memory. It is also suggested that these two experimental animal models may be useful for evaluation of therapeutic drugs for senile dementia of the Alzheimer type.

1692 AMYGDALA DYSFUNCTION IN AUTISM

The anatomic site responsible for infantile autism is unknown. Based upon converging neuropsychological/neuropathological evidence that the temporal lobe may be the primary site of dysfunction in autism, we have adapted discrimination and memory tasks that distinguish amygdalar from hippocampal damage in monkeys (Murray/Mishk in l982). This neuropsychological paradigm was applied to 18 autistic subjects matched very closely to 18 Down's syndrome (DS) controls on the basis of age, sex and scores on the Raven Progressive Matrices. A subject was considered autistic when he/she achieved a score within 1 SD of the mean for the autistic subgroup of a 2,000 subject standardization sample (Autism Behavior Checklist, ABC). On a delayed nonmatching-to-sample task (DNMTS) cross-modal scores correlated with ABC body and object use (r= -0.42, p<0.05) and cross-modal with ABC social and self-help skills (r= -.45, p < 0.05). These correlation scales contain several items in common with the Kluver-Bucy syndrome, a neurobehavioral abnormality in animals and humans associated with damage to the amygdala. On the visual DNMTS, a significant group x task interaction was found (F= 6.68, DF= 2, 34, p < .01) indicating that DS performed better than autistics. Impairment of the visual DNMTS in monkeys results from lesions in both the amygdala and the hippocampus. There were no significant differences observed between the two groups on the spatial location tasks reflective of the hippocampal lesions alone. Taken together, these results suggest a disportionate functional impairment of the amygdala in autism.

Processing of auditory information by the blind in spatial localization tasks.

Spatial localization of sonorous targets in the near space, by blindfolded sighted subjects and by early- or late-blind subjects, was investigated using a two-dimensional coordinate system (direction and distance) in various experimental conditions: The head was free or restrained, and the subject’s response was either a finger pointing on a coordinate grid in open loop or a verbal assessment based on a simple reference system. The results for each group of subjects were processed by dealing separately with distance and direction parameters. They show that with early blinds, only the distance evaluation was particularly impaired. Performance did not seem to depend much on whether the head was restrained or free. Finally, direction was best evaluated by motor responses, whereas distance was more accurately judged verbally.

Selectivity of the evoked potential for vernier offset

Hyperacuity thresholds of a few arc seconds can be achieved psychophysically for a variety of spatial localization tasks. The present experiments show that evoked potentials can be elicited in response to the introduction of vernier offsets, but not by the introduction of other cues to hyperacuity such as bisection or relative pattern motion, although each of these cues is equally salient psychophysically. Moreover, vernier acuity measurements and the evoked potentials elicited in response to vernier offsets are strongly degraded by the introduction of flanking stimuli 2–4 min from the vernier target. This suggests that the hyperacuity VEP is a cortical correlate of a very specific type of hyperacuity, that produced by vernier offsets (colinearity failure).

Long-term changes of orienting behavior in cats with artificial divergent strabismus

Orienting behavior was measured in two monocular spatial localization tasks in normal cats and in cats with artificially induced monocular divergent strabismus. Immediately, and for several weeks after the operation, cats made large “past-pointing errors” with the deviated eye in a direction opposite to the misalignment. These errors were replaced later by “over compensation errors” in the same direction as the strabismus deviation, which persisted for many months after the operation. Over-compensation did not occur when the non-deviated eye was sutured in early life. Electrophysiological measures like grating VEP and A17 single unit responses demonstrated the dominance of the non-deviated eye in the strabismic cats. It is suggested that long-term binocular exposure may lead to a reorganization of visual direction for the deviated eye in divergent strabismus.

Discrepancy and nondiscrepancy methods of assessing visual-auditory interaction.

Much of our information about interaction among the sensory modalities has come from studies in which discrepancy between the modalities has been imposed experimentally. The question arises whether the conclusions generated from discrepancy research are affected by the use of the nonnatural experimental situation: Would the same conclusions be reached if discrepancy were not used? In addition to using the index of interaction derived from discrepancy, as in prior research, the present study assessed two nonexperimentally imposed indices to explore the interaction between vision and audition in a spatial localization task. The additional indices, or “tags,” were standard deviations (SDs) and confidence ratings (CRs) of localization responses. The SD tag showed a pattern of interaction between vision and audition that was identical to that found with spatial discrepancy. The CR tag produced a similar pattern but did not show the same regular variation with the independent variable. Both SD and CR tags showed identical patterns of results when an experimentally imposed discrepancy was and was not used, suggesting that the use of moderate degrees of experimental discrepancy does not produce misleading conclusions about intersensory interaction.

Spatial localization in normal and amblyopic vision

Spatial localization was investigated for each eye of amblyopic observers using a bisection paradigm. The stimuli were comprised of a grating composed of bright lines, and a test line. The test line was either placed above the grating (bisection-no overlap) or within the row of lines comprising the grating (bisection-with overlap) and thresholds for each bisection task were measured as a function of the fundamental spatial frequency of the grating. Vernier thresholds were also measured. For the nonamblyopic eyes at low spatial frequencies, bisection thresholds were a constant fraction (“Weber” fraction) of the space to be bisected, while at high spatial frequencies thresholds were approximately a constant retinal distance (a hyperacuity). However the spatial localization of an amblyopic eye depends upon both the type of amblyopia, and the stimulus configuration. Specifically, for anisometropic amblyopia, spatial localization (bisection-no overlap) and vernier, when scaled to the resolution losses, were normal. However, spatial adjacency (bisection with overlap), while enhancing the spatial localization of nonamblyopic eyes at high spatial frequencies, markedly elevated thresholds in the amblyopic eyes of anisometropic amblyopes. Strabismic amblyopes on the other hand show disturbances in both spatial localization tasks which can not be accounted for on the basis of reduced resolution. Their results are characterized by an absence of a constant Weber fraction at low spatial frequencies and “crowding” effects at high spatial frequencies. For Strabismic amblyopes, the optimal localization thresholds were similar to the Snellen threshold, while for anisometropic amblyopes, the optimal localization thresholds were several times better than the Snellen threshold.

Dissociation of the contributions of the prefrontal cortex and dorsomedial thalamic nucleus to spatially guided behavior in the rat

Rats with lesions of the medial frontal cortex or dorsomedial nucleus of the thalamus (MD) were studied in two spatial localization tasks: the Morris water task and the 8-arm radial arm maze. Rats with medial frontal lesions failed to learn to swim from different locations to a hidden platform located at a specific place in a large tank (Morris task) and were impaired at learning the location of reward in the radial arm maze. Rats with MD lesions were not impaired at spatial orientation in either task. The results provide the first unequivocal evidence of a spatial orientation deficit following frontal lesions and lend support to the notion that the frontal cortex forms part of a ‘spatial mapping system’. The results suggest that although MD is the major afferent to the frontal cortex, it does not provide necessary spatially-relevant input.

Extrageniculostriate vision in the monkey. VIII. Critical structures for spatial localization.

Eight monkeys (Macaca mulatta) were trained on a spatial localization task before and after either total ablation of the striate cortices with partial damage to circumstriate cortices, complete colliculus removals, or combined ablations. The lesions were histologically verified. The task, given under normal room illumination, required the animals to reach for a target randomly placed in one of eight equal segments of a while disk located at arm's length. An apple cube, affixed to the center of the target, served as the reward for accurate reaching. A correct response consisted of an initial contact with either the target or the apple cube directly. The animal was trained sequentially to a criterion level of performance set at 90% correct responses over four 56-trial consecutive sessions using black disks of decreasing diameter (i.e., 90 mm, 55 mm, 35 mm, and 15 mm). Finally, only the apple cube, about 10 mm on a side, was presented. Four animals with complete or almost complete bilateral superior colliculus removals were unimpaired in their performances. The other four subjects with total striate cortex removals could be trained to reach accurately for all targets, but with marked deficits on the first and last tests, i.e., the 90 mm disk and the apple cube. When the striate cortex was ablated in the colliculectomized animals, they failed to attain a criterion level of performance in almost 6,000 trials. These results indicate that the superior colliculus is at least one structure that is critical for spatial localization in the absence of striate cortex, but it is not crucial for this capacity in the otherwise intact animal. In addition, the findings confirmed previous studies which showed that monkeys with total bilateral striatectomies could require the ability to execute accurate visually guided reaches. The present and earlier studies emphasize the primary importance of the geniculostriate system for the function explored and do not support a sharp dichotomy between two independent visual systems in the monkey.

Immediate memory for spatial location.

Performance characteristics in a spatial-location task were examined nonmetrically. In Experiment 1, subjects reproduced the location of a dot either from immediate memory or while actually looking at the dot. Independent analyses of accuracy and the direction of incorrect reproductions yielded evidence for a fast-acting locational-memory process that may be distinct both from locational-perception processes and from response-bias processes. In Experiment 2, three different borders were used to vary the distance between the dot location and the border. Locational-memory accuracy increased as this distance decreased. Incorrect reproductions tended to occur toward rather than away from the border, and the robustness of this effect decreased for dot locations nearer to the border. Due to our nonmetric approach, the above conclusions are generalizable to all psychological conceptions whose spatial distances are monotonically related to the external spatial distances investigated here. A weighted-distortion theory of memory for spatial location is proposed to account for these and other findings.

Response versus place learning by human infants.

Two cross-setional studies examined how infants learn the location of visual events. In Experiment 1, infants of 4, 8, and 12 mo of age learned to turn one way to view a novel pattern. In a subsequent transfer task, they were rotated to face the opposite side of the room. The 4-mo-old infants tended to err by repeating their previously learned response, but within 16-20 trials their performance was comparable to the higher levels maintained by the older infants. These results suggest that young infants learn the location of the pattern primarily in terms of response cues, whereas older infants employ both response cues and place cues. Experiment 2 was designed to independently assess the use of response cues and place cues by infants of 4, 8, 12, and 16 mo of age. All infants were able to rapidly learn and remember the location of the novel pattern when they were given response cues. There was a gradual emergence of place-cue use associated with age. It is suggested that the decrease in infant egocentricity in such spatial localization tasks may in fact reflect an age-related increase in the variety of reliable cues responded to by infants.

Response versus place learning by human infants.

Two cross-setional studies examined how infants learn the location of visual events. In Experiment 1, infants of 4, 8, and 12 mo of age learned to turn one way to view a novel pattern. In a subsequent transfer task, they were rotated to face the opposite side of the room. The 4-mo-old infants tended to err by repeating their previously learned response, but within 16-20 trials their performance was comparable to the higher levels maintained by the older infants. These results suggest that young infants learn the location of the pattern primarily in terms of response cues, whereas older infants employ both response cues and place cues. Experiment 2 was designed to independently assess the use of response cues and place cues by infants of 4, 8, 12, and 16 mo of age. All infants were able to rapidly learn and remember the location of the novel pattern when they were given response cues. There was a gradual emergence of place-cue use associated with age. It is suggested that the decrease in infant egocentricity in such spatial localization tasks may in fact reflect an age-related increase in the variety of reliable cues responded to by infants.

Measures of laterality and theories of hemispheric processes

Experimental data are used to compare four measures of laterality and to examine the relationship of laterality to accuracy on a tachistoscopic visual half-field spatial location task. The four measures are found to be comparable for our data and each measure shows that right hemisphere “dominance” for the task increases with accuracy. The suggestion that such empirical relationships between laterality and accuracy might reflect psychological processes rather than statistical bias is discussed and it is concluded that measures of laterality should be constructed around dynamic theories of the cerebral processes involved in performing a particular task.

Geographic orientation in patients with unilateral cerebral disease

The accuracy of geographic orientation was studied in patients with unilateral cerebral disease and control patients. The influence of educational background on performance was also assessed. When educational background was controlled, the patients with brain disease performed more poorly than the controls on tasks requiring the localization of states and cities on a map of the United States and on a verbal test requiring them to indicate the directional relations between places. Educational background showed both an overall influence on performance level and an interaction with diagnostic category, the less well educated patients with brain disease showing a larger difference from their controls than did patients with better education. A “vector” score, reflecting a shift in localization toward the left or right part of the map differentiated between patients with right and left hemisphere disease and suggested neglect of the visual field contralateral to the side of lesion in some of these patients. The relationship between directional bias in geographic orientation and unilateral neglect in simpler spatial localization tasks remains an open question.