Simulating individual word identification thresholds and errors in the fragmentation task

This article presents a large-scale study that collected word identification thresholds and errors in the fragmentation task for all four-letter French words. In the first part of this article, we identify some of the variables (e.g., word frequency, neighborhood size, letter confusability) that affect performance in the fragmentation task. In the second part, we analyze individual response performance and identify different response strategies. We demonstrate that the interactive activation model can account for individual response strategies by adapting two of its original parameters: word-letter feedback and letter-word inhibition. In the third part, we demonstrate that the adaptation of the interactive activation model to the fragmentation task makes it possible to successfully simulate a facilitatory frequency effect on identification thresholds, an inhibitory neighborhood size effect on error rates, and an inhibitory letter confusability effect on identification thresholds. When the task-specific processes of the fragmentation task are specified and individual response strategies are considered, the interactive activation model provides a parsimonious architecture for modeling the task-independent processes involved in word perception.     

Taste rejection of nonnutritive sweeteners in cats.

Cats reject saccharin and cyclamate and are indifferent to dulcin, although they, like other mammals, prefer sucrose. The rejection threshold for saccharin found in this experiments, .0001 M, is about 2 log steps lower than a previously reported rejection threshold for sodium saccharin. Water produces a taste in cats adapted to their own saliva. The high sodium saccharin threshold may have resulted because the taste of the sodium saccharin was masked by the taste of the water solvent; however, saccharin may also be somewhat more aversive to the cat than sodium saccharin. Saccharin may produce an aversive taste because it stimulates receptor sites sensitive to substances bitter to man as well as those sensitive to sugars. In addition, saccharin may not be an effective stimulus for all sugar-sensitive sites.     

UNDER WHAT CIRCUMSTANCES CAN A UNIONIZED COMPANY USE TESTING FOR PROMOTION?1

A job-related, “fair test” of ability, when used as one tool and not as the sole determining factor, has been established by arbitrators to be an appropriate selection instrument. If a test has been determined as being job-related (i.e., related to the actual performance of the job), has been administered and scored both fairly and consistently, it will be considered a “fair test.” Generally, in unioncompany contracts that mention testing, a “fair test” contains the above qualifications. Arbitrators have indicated that the union involved should be afforded the opportunity to see the test; it was made quite clear, however, that the union should not have the test. In all cases reviewed, tests were upheld by arbitrators when they (1) were “fair tests,” and (2) did not conflict with the contract language. Past testing practice was not a determining factor when these two conditions existed. A total of 69 cases between 1953 and 1967 have been found relevant–27 from 1953 to 1962 and 42 from 1963 to 1967. In the first study, 13 cases were lost by a company; in six of these cases a company violated the union-company contract and in seven cases the test used did not qualify as a “fair test.” A total of twelve cases were lost by a company in the second study; in two cases a company violated the union-company contract and in ten cases the test used did not qualify as a “fair test.”     

Constraints on Pavlovian aversive conditioning: Implications for avoidance learning in the rat

Four experiments investigated the relative degree of control exerted by several conditional stimuli when each stimulus: (a) preceded shock, (b) followed shock, and preceded a shock-free interval, (c) was independent of shock, or (d) was novel. When the onset of an auditory stimulus had preceded shock (Experiments 1, 2A, and 3), it always exerted conditioned excitatory control. When the same stimulus preceded a shock-free interval, it never exerted conditioned inhibitory control. When the onset of light (Experiments 2B, 4), silence (2C), or darkness (1, 2D) preceded a shock-free interval, it always exerted conditioned inhibitory control. However, when one of the latter stimuli preceded shock, it failed to exert excitatory control. Several models of this phenomenon were tested. The implications of these results for the species-specific defence reaction and two-factor theory accounts of avoidance learning were outlined.     

Computational studies of the development of functionally specialized neural modules

Three hypotheses about the activity-dependent development of functionally specialized neural modules are discussed in this review. These hypotheses state that: (1) a combination of structure function correspondences plus the use of competition between neural modules leads to functional specializations; (2) parcellation is due to a combination of neural selectionism, the idea that learning results from a stabilization of some neural connections and the elimination of others, and a locality constraint, which states that connections between nearby neurons are more easily stabilized than those between distant neurons; and (3) a temporal and spatial modulation of plasticity can induce higher functional development in later-developing parts of the nervous system relative to earlier-developing parts. All three hypotheses have been implemented and evaluated in computational models. Limitations of current neuroscientific methodologies mean that computer simulation provides one of the only tools available for evaluating and refining our large-scale theories of the development of functionally specialized neural modules.