Deficits in visual learning produced by posterior temporal lesions in cats.

Eight cats with lesions in the posterior temporal (PT) cortex, 7 cats with lesions in the basolateral amygdala (BLA), and 8 intact controls were observed on 8 tests of visual discrimination learning and spontaneous responses to salient visual stimuli. The effects of the 2 lesions were somewhat dissociable. The PT lesions were accompanied by a severe deficit in pattern discrimination learning but no loss in visual tracking or orientation to the silhouette of a threatening cat. The BLA lesions produced a milder and less consistent loss in pattern discrimination but serious defects in tracking and response to the cat silhouette. Both operated groups performed well on the visual cliff. The deficit from PT lesions appeared independent of damage to the geniculocortical system. The parallel of symptoms from PT lesions in cats and inferotemporal lesions in monkeys is discussed. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual discrimination defects in cats with temporal or occipital decortications.

Investigated performance on visual discrimination problems by 7 control (C) cats, 8 cats with lesions in the posterior temporal (PT) cortex, and 8 with destruction of the central 3-20° of the retina's projection to the marginal (M) gyrus. Group PT was impaired on 7/11 initial learning and transfer tests and on 0/3 retention tests with pattern stimuli and was inferior to Group C on 1/7 object discrimination tasks. No discrimination contingency was more likely than the others to reveal a significant deficit in Group PT. Group M was not impaired relative to Group C on any individual discrimination task. However, it made significantly more total errors on 7 discriminations between complex patterns (embedded or masked figures) than Group C. On 3 discriminations between simple patterns (unmasked figures), Group M made fewer errors than Group C. This pattern of loss is qualitatively similar to but milder than that observed in previous cats with M lesions, probably because the present M lesions were relatively small. Findings indicate that M and PT ablations produce differential impairments in cats, a selective difficulty in differentiating complex patterns after M lesions and a nonselective disruption of pattern discrimination learning after PT lesions. (34 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Posterior extramarginal cortex and visual learning by cats.

Reports results of 3 experiments with a total of 59 mongrel and 11 Siamese cats. Extensive ablations of posterior cortex which spared the primary visual areas severely impaired visual pattern discrimination, detour learning, and spatial reversal performance. Lesions in the posterior ecto- and suprasylvian gyri (EP) produced significant deficits in learning multiple object discrimination problems, repeated reversals on spatial or visual cues, and successive visual discriminations. Ss with cortical ablations that did not invade the EP region but did cause damage to the optic radiations were not impaired in reversal learning and were deficient in successive discriminations only when tested with nonsalient cues. Thus, some of the defects shown by EP cats are qualitatively different from the losses in cats with damage to the geniculostriate system. (39 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of context manipulation on memory and reversal learning in rats with hippocampal lesions.

Conducted 3 experiments with 83 male Long-Evans rats to investigate (a) the memory of hippocampus-damaged Ss, and (b) their ability to modify response strategies in relation to the influence of familiar contextual cues. In Exp I, groups of hippocampal and control Ss learned a simultaneous discrimination habit and were subsequently tested for its retention under variable contextual conditions. All groups recalled the discrimination response to an equally high level when testing conditions were constant throughout, but the hippocampal group showed impaired memory when contextual stimuli at recall testing did not conform to those of original learning. Results of Exp II indicate that the hippocampal impairment was not simply the result of introducing novel stimuli. In Exp III, Ss were administered a reversal learning task with contextual stimuli varied between the 2 tests. The typically observed impairment of hippocampal Ss on this task was reduced by contrasting contextual conditions. Results are seen to support a context-retrieval interpretation of hippocampal function. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rhinal cortex lesions produce mild deficits in visual discrimination learning for an auditory secondary reinforcer in rhesus monkeys.

Aspiration, but not neurotoxic, lesions of the amygdala impair performance on a visual discrimination learning task in which an auditory secondary reinforcer signals which of 2 stimuli will be reinforced with food. Because aspiration lesions of the amygdala interrupt projections of the rhinal cortex traveling close to the amygdala, it was hypothesized that damage to the rhinal cortex would severely impair learning in this task. Rhesus monkeys (Macaca mulatta) were trained to solve visual discrimination problems based on an auditory secondary reinforcer, were given lesions of the rhinal cortex or the perirhinal cortex alone, and were then retested. The monkeys displayed a reliable, albeit mild, deficit in postoperative performance. It is concluded that the aspiration lesions of the amygdala that produced a severe impairment did so because they interrupted connections of temporal cortical fields beyond the rhinal cortex that are also involved in learning in this task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Univariate analysis of tsetse habitat in the common fly belt of southern Africa using climate and remotely sensed vegetation data

We used 5 binocularly deprived cats (BD cats), 4 control cats reared also in the laboratory (C cats) and 4 cats reared in a normal environment (N cats). The cats were trained to discriminate an upward or downward-moving light spot versus a stationary spot (detection task) and then an upward versus a downward spot (direction task). The N and C cats learned slowly. The learning was slower than in previously studied discriminations of stationary stimuli. However, all N and C cats mastered the detection task and except one C cat the direction task. In contrast, 4 BD cats failed in the detection task and all in the direction task. This result is consistent with single-cell recording data showing impairment of direction analysis in the visual system in BD cats. After completing the training the upper part of the middle suprasylvian sulcus was removed unilaterally in 7 cats and bilaterally in 6 cats. Surprisingly, the unilateral lesions were more effective: the clear-cut retention deficits were found in 5 cats lesioned unilaterally, whereas only in one cat lesioned bilaterally.     

Impairment in object-in-place scene learning after uncinate fascicle section in macaque monkeys.

Three previous experiments have shown that a disconnection of frontal cortex from inferior temporal cortex in monkeys impairs a variety of visual learning tasks but leaves concurrent object discrimination learning intact. In the present experiment, three monkeys were trained on an object-in-place task where concurrent object discrimination learning took place within unique background scenes. After surgery to transect the uncinate fascicle, the monosynaptic route between prefrontal cortex and inferior temporal cortex, all three monkeys showed an impairment relative to their preoperative performance. Combined with previously reported impairments after uncinate fascicle transection, the interaction between frontal cortex and inferotemporal cortex is likely to be important in discrimination learning in background scenes because learning depends on associating the visual elements of a scene together with the appropriate choice object. This result adds to recent evidence showing that tasks such as object-in-place learning and conditional learning are impaired after disconnection of frontal cortex from inferior temporal cortex because those tasks require the representation of temporally extended events. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual discrimination by cats given lesions of visual cortex in one or two stages in infancy or in one stage in adulthood.

Sparing of visual function was studied in cats with bilateral cortical damage to Areas 17 and 18 and most of Area 19. Cats with lesions made in 2 stages, on Postnatal (P) Days 3 and 6, in 1 stage on P6, or in 1 stage in adulthood were compared with sham-operated controls on 10 visual discrimination tasks. On some tasks, both groups of cats that underwent surgery as infants showed considerable sparing of function compared with cats that had surgery as adults; the latter group showed a marked impairment. However, on several of the discriminations, 2-stage lesions permitted almost total sparing of pattern vision, whereas 1-stage lesions made neonatally were almost as debilitating as those incurred in adulthood. The findings suggest that differential behavioral consequences can follow physiological or anatomical changes, or both, that occur within a 4-day neonatal interoperative period. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A comparison of discrimination and reversal learning for olfactory and visual stimuli in aged rats.

The present study investigated age-related differences in discrimination and reversal learning for olfactory and visual stimuli in 6-month and 24-month-old rats. Rats were trained to discriminate between two pseudo-randomly selected odors or objects. Once each animal reached a criterion on discrimination trials, the reward contingencies were reversed. Young and aged rats acquired the olfactory and visual discrimination tasks at similar rates. However, on reversal trials, aged rats required significantly more trials to reach the learning criterion on both the olfactory and visual reversal tasks than young rats. The deficit in reversal learning was comparable for odors and objects. Furthermore, the results showed that rats acquired the olfactory task more readily than the visual task. The present study represents the first examination of age-related differences in reversal learning using the same paradigm for odors and objects to facilitate cross-modal comparisons. The results may have important implications for the selection of memory paradigms for future research studies on aging. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Discrimination learning of grating orientation in visually deprived cats and the role of the superior colliculi.

Four cats deprived binocularly of pattern vision (BD cats), 4 control cats reared also in the laboratory, and 4 normal wild cats (NW cats) were trained to discriminate gratings of progressively smaller difference in orientation. Differences in learning were found only in fine orientation discriminations. The stage of 15° orientation difference was learned by 4 NW cats, 2 control cats, and 1 BD cat. After the discrimination training, the superior colliculi were ablated in 2 control cats and 2 BD cats. In contrast to control cats, the BD cats were very deficient and failed to relearn even a horizontal versus vertical orientation discrimination. Thus, an abnormal neural strategy used by BD cats diminished their deficit in grating discrimination learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Critical determinants of nonspatial working memory deficits in rats with conventional lesions of the hippocampus or fornix.

Rats with conventional lesions of the hippocampus or fornix were compared postoperatively with controls on nonspatial memory tasks. Neither lesion impaired delayed matching-to-sample (DMS) performance in a discrete-trial task involving "pseudo-trial-unique" complex stimuli. An impairment emerged if a single pair of complex stimuli was used throughout each day's session, and the greatest impairment was obtained with the use of a single pair of less complex stimuli throughout each day's test. Transfer to continuous DMS task with no explicit intertrial interval produced a different pattern because both lesion and control levels of performance were depressed when 2 complex stimuli were used repeatedly. A final, separate discrimination learning experiment showed that hippocampectomized rats readily discriminated between the stimuli associated with the greatest lesion-induced DMS deficit. Hippocampal dysfunction thus produces clear deficits on nonspatial memory tasks under appropriate test conditions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Eye movements of monkeys during discrimination learning: Role of visual scanning.

In Exps I and II with 7 stumptailed monkeys (Macaca arctoides), Ss were given a series of 2-choice, dot-pattern discrimination reversal problems. Results indicate that the rate of reversal learning was markedly retarded by the experimental condition. The magnitude of the effect was unrelated to the similarity of the uninformative stimulus to the discriminative stimuli. In Exp III, 5 experienced Ss were given a series of discrimination problems without reversals, during half of which the experimental condition was in effect. The results were similar to those of the 1st 2 experiments. In Exp IV (3 experienced Ss), each trial began with uninformative stimuli, which were replaced by the discriminative stimuli when visual scanning occurred. The uninformative stimuli had no clear-cut effect on discrimination learning. Findings indicate that the information provided by above-minimum levels of scanning is not necessary for discrimination learning per se, but it does appear necessary for efficent discrimination learning. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dual task performance after diazepam intake: can resource depletion explain the benzodiazepine-induced amnesia?

It was tested whether a depletion in resources can account for the benzodiazepine-induced memory impairment. In two experiments, it was examined whether dividing attention had a disproportionately detrimental effect on learning semantically related and unrelated word pairs after diazepam intake. Word pairs had to be learned in both a single task condition and while performing a visual discrimination task concurrently (dual task condition). Moreover, the complexity of the visual discrimination task was manipulated systematically. Diazepam (15 mg, orally) or placebo was administered in a double-blind, between-subjects design. Subjects after diazepam intake were clearly impaired in learning unrelated word pairs, but not in learning related word pairs. Dividing attention in the dual task condition was associated with a reduction in learning unrelated word pairs, but this was not disproportionately reduced after diazepam intake. Moreover, the magnitude of resource depletion did not correlate with the severity of the diazepam-induced memory impairment. In general, the pattern of results does not support the hypothesis that a depletion of resources can explain the benzodiazepine-induced memory impairment.     

Early and permanent effects of monocular deprivation on pattern discrimination and visuomotor behavior in cats

Visuomotor behavior and pattern discrimination were studied in a group of cats raised with one eye closed by eyelid suturing 7-10 days after birth. At the age of 8-10 months the animals were forced to use their deprived eye by reversal of eye closure (closing the normal eye and opening the deprived one). Visuomotor behavior and pattern discrimination were tested before as well as after reverse closure, to compare performances of the deprived eye with those of the non-deprived eye. In order to get optimal visuomotor experience, the animals were kept in large playrooms for at least 4h each day. Except for normal tactile placing responses, visually triggered extension responses and uncertain jumping, 2 years after reverse closure all other tests (visually guided reaching, visual cliff behavior, obstacle avoidance, tracking, jumping, and visual blink responses) still showed impairments; the optokinetic nystagmus was asymmetric. In contrast with this partial behavioral recovery, pattern discrimination in a simple nose-push training box requiring no complicated visuomotor coordination was found to be positive. Discriminations of gratings of different orientations, starting 4 weeks after reverse closure, appeared to be normal, in comparison with performance using the non-deprived eye of the same cats tested before reverse closure. Form discrimination was also found to be positive; some monocularly deprived cats required more trails than normal cats in upright vs. reversed solid triangles discrimination, but succeeding form problems were mastered within the same range as found in normal cats. Apparently behavioral defects after monocular deprivation are due to deficiencies in visuomotor control rather than in pattern identification.     

Cholinergic blockade effects on spatial integration versus cue discrimination performance.

Conducted a within-Ss investigation to determine the effects of central vs peripheral cholinergic blockade in 20 male Long-Evans hooded rats tested either on a spatial integration task in which the possibility of rule learning was also available or on a visual discrimination task in which the daily location of food was marked by a distinctive visual stimulus pattern. All testing was conducted on the Maier 3-table apparatus. The only effect of peripheral cholinergic blockade, produced by intraperitoneal atropine methylnitrate (50 mg/kg), was a decrease in exploratory behavior. In contrast, central cholinergic blockade by means of atropine sulfate (50 mg/kg) markedly impaired spatial integration performance. However, it did not impair Ss' ability in rule learning or visual discrimination learning. Central cholinergic blockade impaired Ss' tendency to enter all tables before reentering a given table during the exploratory phase of the daily session. This finding suggests an impairment of working memory for spatial information rather than a general impairment in working memory; this interpretation is applied to the explanation of the deficit in the spatial integration performance. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual mediational instruction: Reducing interference within visual and aural multiple-discrimination tasks.

In two investigations, involving 50 male and 50 female college undergraduate subjects 18–24 years old, we compared differences in the learning of a highly interfering paired-associate discrimination task with and without the use of visual mediational cues. In computerized training, subjects were taught to discriminate between various International Morse Code symbols, given visually and/or aurally, and to respond with the appropriate paired letter of the alphabet. When presented with visual stimuli during a test situation, those subjects taught to use visual mediators significantly increased correct discriminations immediately, as well as 7 and 90 days after training. In addition, when given only aural stimuli during a test situation, those subjects previously trained with visual mediators recalled significantly more correct responses than those receiving training involving only aural or visual stimuli. Visual mediational instruction was shown to significantly reduce interference between the highly similar Morse Code symbols and to facilitate their association with the proper alphabet letter. Further research and applications of mediational instruction are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reversal learning in pigeons: Effects of selective lesions of the Wulst.

Evaluated the effects of bilateral lesions of individual laminae of the Wulst on reversal-learning performance in pigeons. After surgery, Ss were trained to perform a simultaneous color discrimination. Once successful discrimination was achieved, the positive and negative stimuli were reversed, and Ss were again trained to criterion. 20 reversals were carried out. A multiple regression analysis indicated that those components of the Wulst that were critical for increasing the numbers of errors on each reversal were the laminae that receive the thalamofugal visual projections (i.e., the nucleus intercalatus of the hyperstriatum accessorium and the hyperstriatum dorsale). Lesions in the other laminae of the Wulst (the hyperstriatum accessorium and the hyperstriatum intercalatus superior) had no effect on errors. There was no evidence of an increase in either perseverative errors or position habits in the Ss with lesions, suggesting that the reversal deficits were not likely to be due to perseveration, attentional impairment, or inappropriate processing of spatial information. The deficit may have been produced by excessive interference between learning in a given session and learning in previous sessions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reversal set formation in the visually decorticate rat.

Results of 4 experiments with 32 male black-hooded rats show that Ss given large visual cortex lesions demonstrated a simultaneous task reversal deficit previously reported by R. C. Gonzales et al (1964) to follow more extensive cortical ablation. However, no deficit appeared in an operant discrimination that deemphasized visuospatial cues, and the simultaneous task deficit vanished when translucent eye occluders were applied to eliminate spatial, but not intensity, cue use. Because the lesion Ss showed an impairment only when visuospatial cues were available and relevant to correct reversal performance, they seemed hindered by their incompetent processing of visuospatial information. Results support spatial rather than learning approaches to visual cortex function. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Triple dissociation of anterior cingulate, posterior cingulate, and medial frontal cortices on visual discrimination tasks using a touchscreen testing procedure for the rat.

Four experiments examined effects of quinolinic acid-induced lesions of the anterior cingulate, posterior cingulate, and medial frontal cortices on tests of visual discrimination learning, using a new "touchscreen" testing method for rats. Anterior cingulate cortex lesions impaired acquisition of an 8-pair concurrent discrimination task, whereas posterior cingulate cortex lesions facilitated learning but selectively impaired the late stages of acquisition of a visuospatial conditional discrimination. Medial frontal cortex lesions selectively impaired reversal learning when stimuli were difficult to discriminate; lesions of anterior and posterior cingulate cortex had no effect. These results suggest roles for the anterior cingulate, posterior cingulate, and medial frontal cortex in stimulus-reward learning, stimulus-response learning or response generation, and attention during learning, respectively. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attention and relative novelty in human perceptual learning.

Four experiments examined the role of attention in human perceptual learning. In Experiment 1, participants were preexposed to a pair of visual (checkerboard) stimuli AX and BX, with common elements X and unique features A and B. A same-different task was then used to assess discrimination of AX and BX and a pair of control stimuli, CY and DY. In addition, participants' eye movements were recorded to assess the role of attentional processes. The results showed that preexposure enhanced discrimination between AX and BX. Furthermore, participants showed greater attention to the preexposed unique features A and B than to the novel unique features C and D, as measured by the eye gaze monitor. Experiments 2 and 3 examined the prediction that perceptual learning is due to the relative familiarity of the common and unique stimulus features. Experiment 4 replicated the intermixed-blocked effect and showed that the way in which AX and BX are presented is also important for perceptual learning. The results generally support the idea that intermixed preexposure to AX and BX increases attention to the unique stimulus features A and B. Some aspects of the results are consistent with a relative novelty account, whereas others implicate a high-level attentional process that is not driven by stimulus novelty. (PsycINFO Database Record (c) 2011 APA, all rights reserved)