Preference and information about the time and the occurrence of shock delivery

Abstract

Rats given the option to choose between a signaled-shock condition, in which all signals were followed by shock, and one in which extra signals occurred showed no preference for either condition. In contrast, when all signals were followed by shock, rats showed a strong preference for a condition in which shock followed the signal by a fixed, rather than a variable, time duration. The latter result indicates that some types of information about aversive events may be reinforcing.Recent evidence indicates that preference for signaled over unsignaled inescapable shock is importantly controlled, not by the signal that precedes shock, but by stimuli accompanying the signal's absence (discriminable shock-free time or "safe" periods). However , there are conflicting data regarding the role of the signal as a predictor of shock (Arabian & Desiderato, 1975 ; Badia, Harsh , Coker, & Abbott, 1976). Part of this discrepancy could stem from the fact that stimuli which reliably predict shock contain at least two different types of information. The presence of the signal indicates that shock will occur, while the usual fixed temporal relationship between onset of the signal and onset of shock indicates something about when shock will occur. Badia et a1. (1976) manipulated the first source of information by varying the proportion of extra signals and found preference for the signaled over the unsignaled condition to be largely independent of this variable. Arabian and Desiderato (1975), on the other hand, manipulated the second source and found preference for a condition containing less, rather than more, accurate information about the time of shock delivery (but see Collier, 1977). The present research assessed the ability of the two sources of information described above to support preference behavior in a situation where the signal's absence always identified a period free from shock. Thus, any differences in observed responding could be attributed to the reinforcing effects of the signal-shock relationship rather than to stimuli associated with the signal's absence.

The concept of uncertainty in animal experiments using aversive stimulation.

“…The suppression of basal rate of responding was significantly greater in the Random than in the Predictable Group. This finding is essentially in line with the results obtained by Safarjan and D'Amato (1977).…”

“…Safarjan and D'Amato (1977), using a changeover technique, demonstrated that rats strongly preferred a condition in which shock followed the signal by a fixed rather than by a variable time duration. Rats were allowed to make a choice in an operant chamber between the condition in which shocks came invariably at 5 sec after the signal onset (later, at 10 sec after) and the condition in which shocks came between 1 and 26 sec, with a mean of 5 sec, after the signal onset (later, the range was from 1 to 52 sec, with a mean of 10 sec).…”

Choosing between predictable and unpredictable shock conditions: Data and theory.

“…To be maximally effective, preparatory responses must be precisely timed, and conditions that allow this would be preferred to conditions that do not. Evidence supporting this view has been found by Safarjan and D'Amato (1977). This study reports that subjects prefer fixed over variable signal durations.…”

“…Unfortunately, when the assumptions are viewed in this larger context, they often conflict. For example, to account for the choice of immediate over delayed shock conditions and of fixed over variable signal durations, it is assumed that preparatory responses must be precisely timed to coincide with shock (e.g., Knapp etal., 1959;Safarjan & D'Amato, 1977). Presumably, longer delays to shock make precise timing difficult.…”