Excitation and inhibition in unblocking

In four experiments the nature of learning established with unblocking procedures in the appetitive conditioning of rats was examined. Measures of learning included response topography, effects of selective satiation, and summation and retardation tests of conditioned inhibition. One cue (A) was first paired with either a single unconditioned stimulus event, US1, or a sequence of two events, US1----US2. US2 was either qualitatively similar to (US2-Same) or different from (US2-Diff) US1. Then, a compound of A and a novel cue (X) was reinforced with US1 or US1----US2. Conditioning to X was blocked if either the single US1 or the US1----US2 sequence was used in both phases. If X accompanied an upshift in the reinforcer, from US1 to US1----US2, it acquired conditioned responding, especially when US2-Diff was used. Responding in the latter case was the consequence of both X-US1 and X-US2 associations. In Experiments 1-3, if X accompanied a downshift from US1----US2-Same to US1, it acquired conditioned responding that was based on X-US1 associations, but if it accompanied a downshift from US1----US2-Diff to US1, it acquired conditioned inhibition based on X-US2 associations. In Experiment 4, X acquired net inhibition at short US1-US2 intervals and net excitation at longer intervals, with downshifts from either US1----US2-Same or US1----US2-Diff to US1. However, the interval gradient was broader with downshifts from US1----US2-Diff. These data, and several other contradictory findings in the unblocking literature, are consistent with the views that (a) the surprising addition or deletion of US2 in unblocking experiments both facilitates the acquisition of excitatory X-US1 associations and establishes either excitatory or inhibitory, respectively, X-US2 associations, and (b) that the gradient of X-US1 facilitation is broader than that of X-US2 association.     

Characteristics of recovery of drawing ability in left and right brain-damaged patients

Drawings of a "person" were obtained from 21 patients with left brain damage (LBD) and 13 patients with right brain damage (RBD) at hospital discharge and 1 month postdischarge, corresponding to 2-4 and 6-8 weeks postonset, respectively. Early LBD drawings were simplistic and often incoherent. Most were placed in the upper left quadrant of the page. RBD drawings were scattered, fragmented, and elaborately detailed. Many showed evidence of left-sided neglect. The resolution of drawing disability also differed between the two groups: LBD subjects recovered drawing abilities more rapidly and more completely than RBD subjects. These differences in drawing characteristics and in the resolution of drawing disability were discernable for experienced neuropsychologists.     

The effects of satiation after first— and second-order appetitive conditioning in rats

Rats received first- and second-order conditioning based on a food unconditional stimulus (US). The effects of postconditioning satiation on the performance of detailed behavioral components of general activity evoked by first- and second-order conditional stimuli (CSs) were then assessed in extinction tests. Satiation reduced the frequency of all components of general activity evoked by first-order CSs but had little or no effects on behaviors evoked by second-order CSs. These results are consistent with earlier suggestions that first-but not second-order conditional responding is mediated by a representation of the US and that a major effect of satiation is to devalue that representation.     

Reinforcement of eye movement with concurrent schedules

Human macrosaccadic eye movements to two areas of a four-dial display were conditioned by concurrent variable-interval schedules of signals. Reinforcers (signals) were delivered to the two right-hand dials on one schedule and to the two left-hand dials on another, independent schedule. The use of a changeover delay between crossover eye movements and reinforcement had the effect of changing the pattern of scanning from fixating four dials in succession or in a Z-shaped pattern to scanning vertically the dials on either side with fewer crossovers. In the presence of a changeover delay, subjects matched relative eye-movement rates and relative reinforcement rates on each schedule. Rate of crossover eye movements, with a changeover delay in effect, was also inversely related to the difference in reinforcements arranged by the concurrent schedules. The results suggest that for stimuli whose critical components are arranged spatially, conditioned eye movements play an important part in selective stimulus control.     

Sequential effects in absolute judgments of loudness

The effects of preceding stimuli on the judgments of current stimuli were examined in a study using absolute judgments of loudness with feedback. It was found that the response on a given trial was dependent on the stimuli in the preceding sequence of at least five trials. Both assimilation and contrast effects were observed. The form of the dependency of a response on a prior stimulus was a function of the ordinal position of the stimulus in the preceding sequence of trials. The stimulus on the immediately preceding trial had an assimilative effect on the response and preceding stimuli two to five trials removed all showed a contrast effect on a given response. The extent to which these preceding stimuli contributed to the contrast effect was an increasing function of their recency. The reversal of the dependency of the response, from assimilation to the stimulus one trial back, to contrast with the stimuli two and more trials back, indicates a unique function of the immediately preceding stimulus in this task. Since there was a reduction in the variance of responses to those stimuli similar in value to the immediately preceding stimulus, it is proposed that the stimulus and feedback on the last trial were remembered and used asa standardin judging the presented stimulus. A model is presented in which it is assumed that the memory of the magnitude of the immediately preceding stimulus is contaminated in specified ways by prior stimuli in the series. The empirical findings of assimilation and contrastare expected consequences of the proposed memorial processes.     

Rapid recovery from aphasia: a detailed language analysis

The paper presents a daily analysis of the language recovery of a patient who was globally aphasic at the time of her first observation and who had recovered language, as measured by the Western Aphasia Battery, at the time of her discharge 14 days later. The paper emphasizes the relatively regular growth of normal syntactic, lexical, and pragmatic features coupled with similar regular decreases in aphasic features. Observations of both phenomena are necessary to describe language recovery.     

Spontaneous configuring in conditioned flavor aversion

A series of experiments investigated spontaneous configuring using the conditioned flavor aversion paradigm with rat subjects. In Experiment 1, extended training of a two-flavor compound stimulus did not produce spontaneous differentiation of conditioned responding to that compound and its elements. In Experiment 2 we found that extended nonreinforced exposure to a compound stimulus generated spontaneous element-compound differentiation when the elements were later conditioned. Rats that received extended preexposure to the compound showed less conditioned responding to the compound than to either of its elements. However, rats that had not received preexposure to the compound showed greater conditioned responding to the compound than to either of its elements (summation). In Experiment 3, nonreinforced preexposure to the compound stimulus prior to minimal reinforced compound training produced spontaneous compound-element differentiation, but extended reinforced compound training eliminated that differentiation. In Experiment 4, extended partial reinforcement training with a compound produced differentiation of the compound from its elements. Implications of these data for the mechanisms responsible for spontaneous configuring and for the summation assumptions common to most learning theories are discussed.