Hippocampus, cortex, and basal ganglia: insights from computational models of complementary learning systems

We present a framework for understanding how the hippocampus, neocortex, and basal ganglia work together to support cognitive and behavioral function in the mammalian brain. This framework is based on computational tradeoffs that arise in neural network models, where achieving one type of learning function requires very different parameters from those necessary to achieve another form of learning. For example, we dissociate the hippocampus from cortex with respect to general levels of activity, learning rate, and level of overlap between activation patterns. Similarly, the frontal cortex and associated basal ganglia system have important neural specializations not required of the posterior cortex system. Taken together, this overall cognitive architecture, which has been implemented in functioning computational models, provides a rich and often subtle means of explaining a wide range of behavioral and cognitive neuroscience data. Here, we summarize recent results in the domains of recognition memory, contextual fear conditioning, effects of basal ganglia lesions on stimulus-response and place learning, and flexible responding.     

Tactile discrimination, response mode, and interhemispheric communication by learning disabled children.

32 right-handed, learning disabled children aged 8-10 yr., 11-13 yr., and 14-16 yr. were presented a tactile discrimination task. Pairs of fabrics of different or the same texture were presented to the same hand (uncrossed condition) or alternating hands (crossed condition). Discrimination errors were compared using a verbal response mode and a nonverbal response mode. Analysis indicated that the number of crossed errors was significantly greater in the verbal response mode than in the nonverbal response mode for only the youngest children. These results suggest selective attention-activation bias and/or hemispheric processing limitations for younger learning disabled children.     

View-invariant object category learning, recognition, and search: how spatial and object attention are coordinated using surface-based attentional shrouds

How does the brain learn to recognize an object from multiple viewpoints while scanning a scene with eye movements? How does the brain avoid the problem of erroneously classifying parts of different objects together? How are attention and eye movements intelligently coordinated to facilitate object learning? A neural model provides a unified mechanistic explanation of how spatial and object attention work together to search a scene and learn what is in it. The ARTSCAN model predicts how an object's surface representation generates a form-fitting distribution of spatial attention, or "attentional shroud". All surface representations dynamically compete for spatial attention to form a shroud. The winning shroud persists during active scanning of the object. The shroud maintains sustained activity of an emerging view-invariant category representation while multiple view-specific category representations are learned and are linked through associative learning to the view-invariant object category. The shroud also helps to restrict scanning eye movements to salient features on the attended object. Object attention plays a role in controlling and stabilizing the learning of view-specific object categories. Spatial attention hereby coordinates the deployment of object attention during object category learning. Shroud collapse releases a reset signal that inhibits the active view-invariant category in the What cortical processing stream. Then a new shroud, corresponding to a different object, forms in the Where cortical processing stream, and search using attention shifts and eye movements continues to learn new objects throughout a scene. The model mechanistically clarifies basic properties of attention shifts (engage, move, disengage) and inhibition of return. It simulates human reaction time data about object-based spatial attention shifts, and learns with 98.1% accuracy and a compression of 430 on a letter database whose letters vary in size, position, and orientation. The model provides a powerful framework for unifying many data about spatial and object attention, and their interactions during perception, cognition, and action.     

Miniature linguistic systems as tests of the use of universal operating principles in second-language learning by children and adults

This study examined four universal operating principles for first language acquisition proposed by Slobin (1973) and MacWhinney (1978). The applicability of these principles to second-language acquisition was tested by teaching children and adults a miniature linguistic system. The results suggested that the four principles played a major role in the learning of the system by 5- to 7-year-olds but not by adults. Modifications were made in the standard miniature linguistic system technique in order in maximize linguistic naturalness and referentiality. The result was a complex system that could still be taught even to 5-year-olds in the space of a few hours.     

Relationship quality and potentially harmful behaviors by spousal caregivers: how we were then, how we are now. The Family Relationships in Late Life Project

Structured interview data from 142 caregivers (98 wives, 44 husbands) indicate that more depressed caregivers are more likely to treat their spouses in potentially harmful ways. However, consistent with hypotheses derived from communal relationships theory, when the preillness relationship between caregiver and care recipient was characterized by mutual responsiveness to each other's needs (i.e., was more communal), caregivers were less depressed and less frequently engaged in potentially harmful behaviors. These effects were not attributable to demographic factors, amount of care provided, care recipient dementia status, or length of time in the caregiving role. Rather, multivariate analyses suggest that the extent to which premorbid relationships were communal in nature determines whether caregivers perceive their current relationships as rewarding, which, in turn, predicts caregiver depression and potentially harmful behaviors.     

STUDIES IN PREDICTIVE BEHAVIOR: Explorations into predictive judgments based on functional learning and defined by estimation, categorization, and choice

A model for functional learning with a subjective regression which intervenes between stimuli and predictive responses was used. The subject had to predict motion time of a ball rolling down a chute. The estimation experiments showed that (1) the relation between predicted and objective time, is biased in the direction of t _pred= t ², (2) training does not increase the veridicality. In the categorization experiments (1) learning occurred more rapidly with homogeneous categories, (2) transfer was facilitated after training on heterogeneous categories, (3) learning occurred without reinforcement by observation. In a choice experiment two simultaneous processes were studied, functional and probability learning.