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PubMed2001

Learning a grating discrimination task broadens human spatial frequency tuning.

The effect of spatial frequency discrimination learning on spatial frequency detection tuning curves, obtained by a summation to threshold paradigm, has been investigated. Three human observers were exposed to a grating discrimination task for longer than two weeks, and their detection thresholds for compound Gabor gratings were measured before and after this time interval. Discrimination thresholds decreased continuously and substantially during the course of learning, while the spatial frequency detection tuning curves show significant broadening in the posttest. Calculating the discrimination resolution of an ensemble of sensory coding units shows that larger bandwidths lead to better spatial frequency discrimination performance if pattern discrimination rests on multidimensional comparison or one-dimensional scaling of the spatial frequency parameter. Further, it is shown that a multiple-mechanism nonlinear pooling model is capable of explaining the results if plasticity of coding unit bandwidth or adaptive weights of the coding unit responses at the stage of response integration is assumed. The alternative sources of plasticity and the consequences of the findings for psychophysical modeling are discussed.

Computer Simulation↗
PubMedDate not supplied

The cerebellum and learning processes in animals.

In theories of motor learning, the cerebellum is assumed to be the storage site of the engram. Recent evidence is presented that the cerebellum, in addition to its mediation of learning of simple motor responses, has a role in cognitive behaviors. For this type of learning, it is possible that the storage site is not the cerebellum, but cerebellar target areas. The possible role of the cerebellum in spatial learning and discrimination learning is emphasized. Ascending cerebellar afferents to fronto-parietal association cortex, the limbic system and the superior colliculus and feedback loops from these areas may be the anatomical basis underlying cerebellar modulation of spatial learning. In regard to discrimination learning, the possible significance of pathways arising from the visual cortex to pontine nuclei projecting to the cerebellar hemispheres must be evaluated. Although much remains to be resolved, the cerebellum seems to contribute to various emotions such as fear, the neural basis of which being cerebellar contributions to the reticular activating system, the limbic system and two-way hypothalamo-cerebellar connections.

Animals↗
PubMed1964

EFFECT OF PRIOR PAVLOVIAN DISCRIMINATION TRAINING UPON LEARNING AN OPERANT DISCRIMINATION.

The effect of Pavlovian discrimination training with two stimuli upon subsequent learning of an operant discrimination involving those stimuli was studied. After preliminary lever press training, the lever was removed and thirsty rats received noncontingent pairings between S(1) (a tone or a clicker) and water reinforcements, whereas S(2) (a clicker or a tone) occurred always without reinforcement. This procedure presumably established S(1) as a positive CS for respondent behavior, whereas S(2) was established as an inhibitory CS. Following this training, the lever was reintroduced and the rats were trained on an operant (lever pressing) discrimination involving S(1) and S(2). For the Consistent Ss, S(1) was the S(D) and S(2) the S(Delta) in the operant discrimination; for the Reversed Ss, S(2) served as S(D) and S(1) as S(Delta). The Consistent Ss learned the operant discrimination significantly faster than did the Reversed Ss. The result emphasizes the importance of respondents, conditioned to S(D) and S(Delta), which modulate operant performance to these stimuli.

Conditioning, Operant↗
PubMed2002

Nucleus accumbens dopamine and discriminated approach learning: interactive effects of 6-hydroxydopamine lesions and systemic apomorphine administration.

RATIONALE: Although dopaminergic mechanisms have been implicated in incentive motivational processes, their role in appetitive conditioning remains poorly understood. OBJECTIVES: To investigate the effects of dopamine (DA) depleting lesions of the nucleus accumbens and the direct acting dopamine receptor agonist apomorphine on the learning of discriminated appetitive approach behavior in a Pavlovian autoshaping paradigm. METHODS: Rats received bilateral infusions of either phosphate-buffered saline (shams) or 6-hydroxydopamine (lesions) directly into the nucleus accumbens. Ten days later, rats were trained on an autoshaping task whereby a previously neutral light stimulus was paired with food reward. Presentation of another stimulus (CS-) was never followed by reward. Over 100 pairings subjects developed a conditioned response of approaching the reward-predictive stimulus (CS+). Prior to each autoshaping session subjects were administered either saline (1 ml/kg SC) or apomorphine (30 microg/kg; 100 microg/kg), in a between-subjects design. RESULTS: Lesioned subjects showed a delay in the acquisition of discriminated approach and were insensitive to a subsequent change in the contingency of the task whereby approaches to the CS+ now prevented food delivery. Low dose apomorphine profoundly impaired learning in both sham and lesioned subjects. Despite increasing the overall number of CS+ and CS- approaches, the higher dose of apomorphine allowed discriminated approach in sham-operated animals only. CONCLUSIONS: These data are compatible with the hypothesis that nucleus accumbens dopamine serves to energize rather than guide conditioned approach to appetitive cues. They also support the notion that DA inputs in this region confer flexibility of approach to cues predictive of reward.

Animals↗
PubMed2002

Attentional control in learning to discriminate bars and gratings.

Transfer effects of learning a spatial-frequency and a bar-width discrimination task on the performance in three other discrimination tasks (relative bar position, local width, and global-size discrimination) have been investigated. In the spatial-frequency discrimination learning task, subjects were trained with grating stimuli which varied in spatial frequency, relative bar position, and grating patch size, but only spatial frequency was relevant for discrimination. The bar-width discrimination learners had to judge the width of single grating bars appearing at random positions distributed around a display center. During the course of 10 consecutive days, all subjects showed a significant reduction of discrimination thresholds. Regarding learning transfer, we find that practicing the spatial-frequency discrimination task yields quite strong improvement of bar-width discrimination and, vice versa, learning bar-width discrimination also leads to strong improvement of spatial-frequency discrimination performance, indicating involvement of coding pathways which are shared by both tasks. On the other hand, there is no performance improvement when subjects do different tasks (grating patch size and relative bar position discrimination) with the same stimulus material as the learning stimuli. The finding of task-driven selective learning for only one local stimulus attribute among other local and global attributes shows that feature-based attentional preselection of basic stimulus attributes is involved in learning. Moreover, differential learning effects for two different local stimulus features indicate that, governed by top-down control, different neural pathways starting from the same low-level code base may be formed in the course of discrimination training.

Attention↗
PubMed1988

Effect of the dietary alpha-linolenate/linoleate balance on lipid compositions and learning ability of rats. II. Discrimination process, extinction process, and glycolipid compositions.

Donryu strain rats through two generations were fed semi-purified diets supplemented with safflower seed oil (rich in linoleic acid) or with perilla seed oil (rich in alpha-linolenic acid), or a conventional laboratory chow (normal control diet). Brightness-discrimination learning ability was determined to be the highest in the perilla oil-fed group, followed by the normal group, and then by the safflower group, extending our earlier observation in a different strain of rat that alpha-linolenic acid is a factor in maintaining high learning ability (Yamamoto, N., M. Saitoh, A. Moriuchi, M. Nomura, and H. Okuyama. 1987. J. Lipid Res. 28: 144-151). After the brightness-discrimination learning test was administered, extinction of learning was measured. The time required for extinction was significantly longer in the safflower group than in either the perilla group or the normal diet group. Thus, the dietary alpha-linolenate/linoleate balance affected both the learning and the extinction of learning. The glycolipids of the cerebrum, cerebellum, and olfactory lobe were analyzed. Although the fatty acid compositions of the sulfatide and gangliosides were significantly different in the three parts of the brain, relatively little difference was observed in the fatty acids of glycolipids between the safflower group and the perilla group, suggesting that gross changes in brain glycolipids are not responsible for the differences in learning abilities between these dietary groups.

Animals↗
PubMed1984

Complex visual discrimination of tridimensional patterns in rats: progressive learning improves discriminative and recognition capacities.

The purpose of these experiments was to evaluate the rat's discriminative capacities when facing tridimensional patterns. The behavioral approach involved 3 steps: (1) After establishing a brightness discrimination in a Y-maze (S+ = dark, S- = bright), tridimensional objects were introduced into the goal boxes. (2) Brightness differences were gradually attenuated during the course of the fading procedure and correct responding to the tridimensional patterns was obtained. (3) This procedure had a second fading phase where configurational differences between these patterns were progressively reduced. All animals trained with this method of successive approximations learned the discrimination to a 90% criterion; whereas control animals, given the same complex discrimination without any shaping procedure, failed to learn. These experiments show that success or failure in the acquisition of a visual task is specific to the training method used. Our fading procedure produced complex discrimination behavior.

Animals↗
PubMed1977

Limbic and prefrontal contributions to somesthetic learning in monkeys.

Monkeys with forebrain commissurotomies and either lateral temporal, medial temporal, dorsal prefrontal, or ventral prefrontal removals from the right hemisphere were compared with control animals in learning tactual discriminations and reversal with the left hand. The lateral temporal removal yielded no effect, confirming the modality-specific roles of this sector in audition (superior temporal gyrus) and vision (inferior temporal gyrus). The dorsal prefrontal removed yielded a deficit in discrimination learning, possibly as a result of the contralateral sensory neglect or the spatial disorder produced by this lesion. Each of the two remaining lesions, medial temporal and ventral prefrontal, yielded deficits in both discrimination learning and reversal; and the effects of combined removal of these two limbic sectors appeared to be additive. Taken together with earlier findings in vision and audition, the results indicate that the two limbic sectors contribute to learning in all sensory modalities, and that they do so through cortico-cortical interaction with the sensory systems.

Animals↗
PubMed1985

Behavior and neurobehavioral teratology using the ferret.

A behavioral profile of the ferret is presented for those who would like to use this animal in behavioral teratology and toxicology, or other disciplines involving behavior. We have reviewed neurobehavioral teratology of lisencephalic ferrets and neuropsychology of ferrets sustaining frontal lesions, as well as most of the studies of "normal" ferret behavior that have appeared in the research literature. Emphasis is placed on discussion of the tests used and how ferrets behaved on them. The behaviors discussed include spatial (maze) learning, delayed response, visual discrimination learning, discrimination learning sets, schedule maintained behavior, shock avoidance learning and spontaneously occurring behaviors, such as ambulation in open field, spontaneous alternation and species specific behaviors. Although the use of the ferret in behavioral experiments is not yet extensive and large gaps exist in our knowledge about the basic functional capacities of this animal, the ferret is unquestionably well suited for behavioral studies.

Age Factors↗
PubMed1996

Learned olfactory discrimination of amino acids and their binary mixtures in bullhead catfish (Ameiurus nebulosus).

The question of whether bullhead catfish can discriminate binary mixtures of amino acids from the individual components of the mixture was investigated. Two groups of catfish were conditioned to different binary mixtures of L-norvaline (NVAL) and L-leucine (LEU). The concentrations of the amino acids in the conditioned mixtures were adjusted so that in different mixtures either NVAL or LEU was the more stimulatory component. Bullhead catfish were unable to discriminate the more stimulatory components, but were able to discriminate the less stimulatory components and other amino acids from the conditioned mixtures. The third group of bullhead catfish was conditioned to L-proline (PRO) and the responses to different mixtures of PRO and NVAL were subsequently evaluated. Behavioral and electrophysiological (EOG) experiments indicated that the difference in relative stimulatory effectiveness levels between NVAL and PRO is > 30,000 times. For subsequent tests, the concentrations of PRO and NVAL were adjusted to form binary mixtures in which PRO and NVAL, respectively, were the more stimulatory components. Bullhead catfish conditioned to PRO discriminated the mixture if NVAL was the more stimulatory component, but did not discriminate PRO from the mixture if PRO was the more stimulatory component. These results suggest that binary mixtures of amino acids are initially perceived as the more stimulatory components of the mixture.

Amino Acids↗
PubMed1994

Learned olfactory discrimination versus innate taste responses to amino acids in channel catfish (Ictalurus punctatus).

Intact channel catfish conditioned to the L-amino acids, proline, arginine, alanine, and lysine, discriminated these stimuli from all other amino acids tested. Behavioral structure-activity tests indicated that L-pipecolate was the only effective agonist of the L-proline conditioned response. For channel catfish in which one of the paired olfactory organs was surgically removed, the number of turns to the conditioned stimulus was 40% fewer than those of intact catfish; however, these semiosmic channel catfish discriminated the conditioned from nonconditioned stimuli, as evidenced by their responding to the conditioned amino acid, with a two- to threefold greater number of turns than to the nonconditioned amino acids. Irrespective of the number of conditioning trials attempted, catfish with both olfactory organs removed were unable to discriminate the conditioned from the nonconditioned stimuli.

Amino Acids↗
PubMed2001

At what age do children learn to discriminate between act and actor?

Children's ability to make moral judgements about an act on the basis of aspects of the act rather than on liking and preconceived ideas about the actor was investigated. 85 children of 4 age groups (preschool, Grades 1, 2, and 3, age range 5-9 years) participated. Act/Actor discrimination was investigated with a test consisting of 8 cartoons. In 4, a rabbit was behaving aggressively against a wolf; the other 4 portrayed identical acts with the wolf as aggressor and the rabbit as victim. Participants made moral evaluations of each cartoon. IQ was measured with Raven's Standard Progressive Matrices, and the general level of moral development was measured in accord with Piaget's (1932) criteria. Age, IQ, and general moral development correlated with discriminative ability for Act and Actor. In Piagetian terms, children at the heteronomous level were not capable of such discrimination, while children at the autonomous level (above 7 years of age) in general were.

Age Factors↗