Impact of Vestibular Lesions on Allocentric Navigation and Interval Timing: The Role of Self-Initiated Motion in Spatial-Temporal Integration

Bilateral intratympanic sodium arsenate injections (100 mg/ml in isotonic saline) in adult male Long Evans rats produced impairments in allocentric navigation using a 12-arm radial maze procedure as well as a motor test battery designed to evaluate vestibular function. In contrast, no impairments in the accuracy or precision of duration reproduction using 20-s and 80-s peak-interval procedures were observed when both target durations were associated with the same lever response, but distinguished by signal modality (e.g., light or sound). In contrast, an ordinal-reproduction procedure with 800, 3200, and 12,800 ms standards requiring the timing of self-initiated movements during the production phase revealed large impairments in the accuracy and precision of timing for vestibular lesioned rats. These impairments were greater on trials in which self-initiated body movements (e.g., holding down the response lever for a fixed duration) were required without the support of external stimuli signaling the onset and offset of the reproduced duration in contrast to trials in which such external support was provided. The conclusion is that space and time are separable entities and not simply the product of a generalized system, but they can be integrated into a common metric using gravity and self-initiated movement as a reference.

The Role of Response-Reward Correlation in Stimulus-Response Overshadowing

Rats pressed levers for food reward which was delivered, when appropriate, 0·4 s after the response. For one group, the delay interval was filled by a light cue; for the other group, the same number of lights was given but they were not correlated with food delivery. In Experiment I, all lever presses were reinforced and there were no differences in response rate between groups. In Experiments II and III, lever pressing was rewarded according to a VI and VR schedule respectively. Group differences were observed in Experiment II but they disappeared in Experiment III. The results of Experiments I and II show that a reward-related stimulus does not overshadow a lever response unless the stimulus is a better predictor of reward. Differences in salience or competition from sign-tracking behaviors were ruled out as causes of this phenomenon. Experiment III demonstrated, however, that a weak response-reward correlation is not a sufficient condition for the overshadowing effect. A fourth experiment replicated the results of Experiment III using naive animals. The results of these last two experiments are not consistent with an information theory approach unless (a) a response-units concept is adopted or (b) the cue involved in overshadowing is not the pre-food light but the end of a temporal interval, whose salience is enhanced by the light.

Children's Response Speeds and Perseverative Responses following Failure as a Function of Instructions and Interresponse Interval

Nonreward has been found to facilitate subsequent responding in a number of experiments with children whereas failure has consistently resulted in a decrement in performance. Two variables confounding comparisons of nonreward and failure studies are (a) the use of constant interresponse intervals of 5 sec or longer in nonreward studies as compared with the use of 0-sec. intervals in most failure studies and (b) the use of other-blame instructions in nonreward studies and self-blame instructions in failure studies. In the present experiment 18 second- and third-grade children were assigned to each of six conditions formed by the factorial combination of constant interresponse intervals of 0, 4, and 8 sec, and self-blame vs other-blame instructional sets. On each trial the subjects performed a light-switching task followed by a lever-pulling response. They were failed prior to completion of the light-switching task on one-half of the 20 trials. Lever-pulling responses following failure were slower than responses following success in the 0-sec. condition but not in the 4- or 8-sec. condition, and response speeds in the 0-sec. condition on failure trials were slower than speeds on 4- and 8-sec. condition failure trials. Decrements in response speeds following failure were found in both the self-blame and other-blame conditions although the decrement was greater in the former than the latter condition. In addition self-blame subjects made more perseverative responses on the light switching game than other-blame subjects. The results were discussed in terms of the effects of interresponse intervals and instructional set on the extent to which responses produced by failure would occur and interfere with the lever response.

Approach-escape interactions in rat brain

Animals with electrodes implanted at tegmental escape points and at hypothalamic approach points were tested for positive reinforcement during simultaneous negative stimulation, and for escape behavior during simultaneous positive stimulation. The test of positive reinforcement was made by presenting a correlated hypothalamic stimulus after each lever response, during a 2-min period, while a constant train of stimulation was being applied to a negative reinforcing point in tegmentum. The test of negative reinforcement was made by presenting repeated 1/2-sec trains of tegmental stimulation at a rate of 1/sec and interrupting this sequence for 4 sec after each lever response, during a 2-min period, while a constant train of stimulation was being applied to the positive reinforcing point in lateral hypothalamus. The constant negative train impeded and sometimes inhibited completely the positively reinforced behavior. The constant positive train, however, far from impeding the escape response, regularly facilitated the negatively reinforced behavior. The data were interpreted on the theory of a one-way inhibition from tegmental escape points to the hypothalamic approach one.