Rats were shocked at the rate of two per minute until they pressed a lever. In Experiment I, shocks were delivered at variable-time intervals averaging 30 sec; in Experiment II, shocks were delivered at fixed-time intervals of 30 sec. A response produced an alternate condition for a fixed-time period. The shock frequency following a response, calculated over the whole alternate condition, was two per minute. The pattern of shocks in the alternate condition was controlled so that the first shock occurred at the same time as it would have occurred had the response not been emitted; the remaining shocks were delayed until near the end of the alternate condition. Bar pressing was acquired in both experiments. This finding is not explained by two-factor theories of avoidance and is inconsistent with the notion that overall shock-frequency reduction is necessary for negative reinforcement. The data imply that responding is determined by the integrated delays to each shock following a response versus the integrated delays to shock in the absence of a response.Key words: aversive control, avoidance, delayed shock, shock frequency, bar press, rats A response on a free-operant avoidance schedule (Sidman, 1953) interrupts for several seconds (RS interval) a series of brief shocks spaced a few seconds apart (SS interval). A single response has two effects. It introduces a delay between the response and the next shock, and it reduces the overall frequency of shocks. Several investigators have attempted to determine which of the two, delay or reduced frequency, is necessary and which is sufficient to produce responding.Lambert, Bersh, Hineline, and Smith (1973) presented rats with a 10-sec stimulus followed by five shocks. A response during the stimulus produced one immediate shock, but caused the five shocks at the end of the stimulus to be omitted; thus, a response resulted in a decreased delay to shock and an 80% reduction in the total number of shocks. Several animals showed increased shuttle responding under this procedure; two rats, however, showed no acquisition of a bar-press response. Lambert ' Hineline's (1970) procedure. When a bar press delayed a single shock for 10 sec, but left the total number of shocks unchanged, the bar press was acquired. Hineline also found that responding stopped when it led to a 10-sec delay to shock accompanied by a shock-frequency increase. Gardner and Lewis (1976)

No abstract

In the absence of responding, pigeons were shocked under a variable-time schedule. Responses on either of two keys occasionally produced one minute of shock-free time. That is, pigeons' key pecks were reinforced with shock-free time under concurrent variable-interval schedules. The relative frequency of access to the one-minute shock-free periods was systematically manipulated. Pigeons tended to match both relative response rate and proportion of time spent on each key to the relative frequency of the shock-free periods. A best-fit linear regression equation accounted for over 95% of the variance in both relative response rate and time allocation. The data paralleled closely the results of concurrent schedules of positive reinforcement. These findings are consistent with a description of reinforcement as a transition to a higher-valued situation and suggest that common laws govern choice for both positive and negative reinforcement.

Previous research has shown that presenting response-independent positive reinforcers reduces the response rate of an operant maintained by positive reinforcement. The present experiment investigated a similar effect using shock-free time as a negative reinforcer. Brief shocks were delivered in the presence of a distinctive stimulus, and pigeon's key pecks were reinforced by the occasional presentation of a 2-minute shock-free period. Extra 2-minute shock-free periods were added independently of behavior. For each of three pigeons, response rate during shock-on periods declined with added shock-free periods; the more frequently the extra shock-free periods occurred the greater the decline in response rate. This outcome is predicted by extending the Law of Effect to include negative reinforcement.

[1] The classification of high frequency (HF) radar backscattered signals from the ionospheric irregularities (clutters) into those suitable, or not, for further analysis, is a time-consuming task even by experts in the field. We tested several different feedforward neural networks on this task, investigating the effects of network type (single layer versus multilayer) and number of hidden nodes upon performance. As expected, the multilayer feedforward networks (MLFNs) outperformed the single-layer networks. The MLFNs achieved performance levels of 100% correct on the training set and up to 98% correct on the testing set. Comparable figures for the single-layer networks were 94.5% and 92%, respectively. When measures of sensitivity, specificity, and proportion of variance accounted for by the model are considered, the superiority of the MLFNs over the singlelayer networks is much more striking. Our results suggest that such neural networks could aid many HF radar operations such as frequency search, space weather, etc.