The effects of escape conditioning and shock intensity on responding during inescapable shock

Eight albino rats, conditioned to press a lever to escape shock, continued to lever press during short inescapable shocks presented subsequently. The rate of this behavior was found to be higher for higher shock intensities regardless of the order in which shock values were presented. Relative to the immediately preceding escape rate, responding during inescapable shock was higher following conditioning at higher fixed-ratio escape requirements. Four subjects not conditioned to escape shock pressed the lever very infrequently during inescapable shock and showed little change with changes in shock intensity. The escape conditioning effects suggest that responding during inescapable shock is superstitious escape behavior. The effects of shock intensity on this behavior appear to be similar to reported effects of shock intensity on escape behavior.     

DRL escape: effects of minimum duration and intensity of electric shock

Three dogs were exposed to a DRL-escape procedure that required them to endure a minimum duration of electric shock without responding in order for a response to terminate that shock. When this minimum duration increased from 0 to either 2.25 or 7.00 sec, response latencies increased proportionately. With the minimum duration held constant at 2.25 sec, a gradual increase in shock intensity to 5.0 ma had no systematic effect upon latencies. Even under the highest shock intensity, 5.0 ma, latency and interresponse-time distributions were unimodal with very few latencies and interresponse times less than the minimum duration. Three additional dogs were exposed to an escape procedure in which every response was immediately reinforced. For these subjects, the same increase in shock intensity to 5.0 ma was accompanied by a decrease in latencies. The precise temporal spacing of responses obtained with the DRL-escape procedure may in part be due to the fact that every response latency and interresponse time that did not meet the minimum duration was not only extinguished but was also punished.     

Prior expectancy and behavioral extremity as determinants of attitude attribution

In an experiment on attitude attribution, subjects were instructed to estimate the “true attitude” of a target person after reading an essay in which he took one or the other side of a controversial issue (legalization of marijuana). Four independent variables were manipulated: the direction of the essay (pro- versus anti-legalization), its extremity (strong versus weak), freedom to choose position versus assignment to position (choice versus no choice), and prior expectancy (expect pro versus expect anti). All experimental predictions were confirmed by the results. When the essay was strong: (1) attitudes were attributed more in line with behavior under choice than under no choice conditions; (2) even under no choice conditions, the target person was seen as believing to some extent in the arguments of his essay; (3) the role of choice was especially prominent when the position of the essay was unexpected. In both strong and weak essay conditions, (4) the behavior was ignored in favor of prior expectancy in no choice conditions, but a contrast effect was observed in the choice conditions. When the essay was weak: (5) subjects attributed the opposite attitude under no choice conditions; under choice conditions, the weak essay was construed as moderate endorsement. As in previous experiments, there was considerable variability in those conditions in which the target person wrote an essay under no choice instructions endorsing the position he presumably opposed. In a second experiment, attempting to determine what produced this variability, it was found that subjects with generalized expectancies of internal control (Rotter, 1966) were more sensitive to variations in choice than were subjects whose expectancies were externalized. Under no choice conditions, “internals” were more inclined to ignore the essay and go by their prior expectancies in attributing attitude; “externals” seemed more impressed by the essay itself.     

Role of fear in mediating shuttle escape learning deficit produced by inescapable shock

The relation between the shuttlebox escape deficit produced by prior inescapable shock (IS) and fear during shuttlebox testing as assessed by freezing was investigated in rats. IS rats learned to escape poorly and were more fearful than either escapably shocked subjects or controls, both before and after receiving shock in the shuttlebox. However, fear and poor escape performance did not covary with the manipulation of variables designed to modulate the amount of fear and the occurrence of the escape deficit. A 72-hr interval between IS and testing eliminated the escape deficit but did not reduce preshock freezing. Diazepam before testing reduced both preshock and postshock fear in the shuttlebox but had no effect on the escape deficit. Naltrexone had no effect on fear but eliminated the escape deficit. This independence of outcomes suggests that the shuttlebox escape deficit is not caused by high levels of fear in IS subjects.     

Choice for signalled over unsignalled shock as a function of shock intensity

Choice between a signalled shock schedule and an unsignalled one was examined at various shock intensities. Three rats were given the opportunity to change from the unsignalled schedule to the signalled one at intensity values between 0.15 mA and 1.0 mA. Steps were usually 0.15 mA and both ascending and descending series were given. For two other rats, shock intensity increased from 0.20 mA to 1.0 mA in 0.20-mA increments; for two additional rats, shock intensity was first 3.0 mA and was then reduced to 1.0 mA. Subjects tended to remain in the unsignalled schedule at the lower shock intensities, but spent most of each session under the signalled schedule at the higher intensities (1.0 mA and 3.0 mA). In addition, the time spent in the signalled schedule tended to vary systematically with shock intensity over at least part of the range of intensity values. It was concluded that the relationship between shock intensity and choice behavior is similar to the relationship between intensity and behavior in procedures involving avoidance, escape, and punishment.     

Prior exposure to inescapable electric shock in rats affects extinction behavior after the successful acquisition of an escape response

In Expt 1, rats exposed to 64 inescapable electric shocks in a restrainer or merely restrained were later given either 0, 5, 15 or 30 escape/avoidance training trials with a two-way shuttlebox procedure that does not lead to interference with escape acquisition due to prior exposure to inescapable shock. After escape training all rats were given an escape/avoidance extinction procedure in which shock was inescapable. The rats which had received prior exposure to inescapable shock responded less often and with longer latencies in extinction than did the restrained rats. Experiment 2 demonstrated that this effect is caused by the inescapability of the initial shock treatment. These results were explained in terms of (a) associative interference which minimized the effect of shuttlebox escape training for the preshocked subjects, and (b) a stronger tendency to recognize the presence of an inescapable shock situation during extinction for the preshocked subjects. The relationship between these results and previous work demonstrating that exposure to the escape contingency mitigates the effects of inescapable shock exposure was also discussed.