Stanley R. Scobie

Stimulus modality and short-term memory in rats

Two experimental paradigms are presented aimed at determining the retention of auditory and visual information over brief delay intervals. First, a conditional delayed matching-to-sample procedure was used in which rats were required to symbolically match the modality of the sample stimulus with one of two comparison stimuli. In the second experiment, subjects were trained and tested using a Konorski-type procedure. Despite the conceptual and procedural differences between the two procedures, subjects in both experiments showed steeper forgetting functions for visual events than for auditory events, while performance levels at 0-sec delay intervals were equivalent for both stimuli. These results, when taken together with related research conducted with pigeons, suggest that content of memory may have important influences on the short-term retention abilities of animal subjects.

Age-related differences in electric shock detection and escape thresholds in Sprague-Dawley albino rats.

For both male and female Sprague-Dawley albino rats, shock detection thresholds decreased as a function of age over a range of 90 to 660 days of age. Shock escape thresholds also were found to vary inversely with age. The findings are discussed in light of previous shock threshold experiments and in terms of implications for studies of age-related learning changes.

Negative contrast in goldfish (Carassius auratus)

Goldfish in a successive differential discrimination displayed strong negative contrast. A successive nondifferential shift in reward magnitude did not produce clear negative contrast, however. Response speed changed appropriately when reward magnitudes were changed. There was no indication of positive contrast in either condition.

Detection, reaction, escape, and debilitation thresholds for electric shock in goldfish☆

Abstract Reception of electric shock by small goldfish was studied with psychophysical methods. Shock intensity was specified as the gradient in volts/centimeter between the shock electrodes. Changes in current density in the water due to resistance changes had negligible effects upon several measures of reaction to shock. Absolute thresholds for an observable motor reaction were higher with the fish parallel to the electrodes than with a perpendicular orientation. These reaction thresholds were essentially identical to detection thresholds determined in an instrumental avoidance situation. Escape thresholds were substantially higher than reaction and detection thresholds. Changes in shock duration had little effect on any of these thresholds. There was a fairly wide range of motivationally significant shock intensities. Exposure to strong shock did not seem to have any long-lasting effects.

Positive behavioral contrast, autoshaping, and omission responding in the goldfish (Carassius auratus)

Two experiments with goldfish were performed to investigate the role of stimulus-reinforcer vs. response-reinforcer relationships in omission training and the role of stimulus localizability in a positive behavioral contrast paradigm. The directed behavior of fish, like that of pigeons and rats in other studies, was greatly influenced by positive stimulus-reinforcer correlations, as evidenced by maintained contacts of a signal for food, even though such responses terminated the signal and cancelled reinforcement delivery. Goldfish exhibited positive behavioral contrast when the signals for reinforcement and nonreinforcement were displayed directly on the response key, but no contrast was observed when variations in a diffuse houselight stimulus were used as signals for reinforcement or nonreinforcement. Analysis of sequential-trial data yielded effects analogous to Pavlovian positive and negative induction. Theoretical and methodological problems were briefly considered.

Avoidance extinction in goldfish

Abstract Independent groups of goldfish trained to avoid shock in a shuttlebox situation were presented with several extinction procedures in which the relationships between the conditioned stimulus and shock were altered and/or response contingencies removed. Random shock presentations, equivalent to the number of shocks received during avoidance acquisition, resulted in response decrements similar to those obtained when the conditioned stimulus was presented alone. Pairing the conditioned stimulus with shock on every trial, however, served to maintain response levels. When response-contingent punishment was superimposed upon these Pavlovian pairings, performance was facilitated slightly although punishment alone resulted in somewhat faster response reduction than that produced by exposure only to the conditioned stimulus. Extinction of avoidance responding produced by exposure to the conditioned stimulus alone was dependent on the total duration of exposure and independent of both number of stimulus onsets and response prevention. These experiments demonstrated that, in general, the procedures used to reduce avoidance responding in rats were equally effective for goldfish, with one exception: the introduction of a Pavlovian contingency following avoidance acquisition, making the previously avoidable shock unavoidable, maintained response probabilities near previously established levels.

Unconditional stimulus intensity and cardiac conditioning in the goldfish (Carassius auratus)

Abstract Independent groups of small restrained goldfish were given pairings of an illumination increase CS and shock USs of different intensities. The relation between conditioned cardio-deceleration and US intensity was a simple monotonic one with an apparent asymptote between 1.3 and 2.2 V/cm. There was no sign of cardio-acceleration at any point in adaptation, conditioning, or extinction. Baseline heart rate was little affected by conditioning but post US rate decreases mirrored the conditioned decreases.

The response-shock interval and conditioned suppression of avoidance in rats*

Rats were trained to avoid unsignaled shocks with response-shock intervals of 30, 60, or 120 sec. When CSs of 60 sec duration paired with unavoidable shocks were then superimposed upon the avoidance baseline, responding decreased during the CS. Reductions in responding resulted in extra shocks which were potentially avoidable in all response-shock interval conditions, with the greatest increase in shocks in the response-shock 30-sec condition. Decreases in responding were greater when the CS was paired with a 2.0-mA unavoidable shock than with a 1.0-mA shock.

Differential reinforcement of low rates in goldfish

Four fish were trained under several values of a differential reinforcement of low rates schedule. Overall rate of responding decreased as the delay period increased. Relative rate of responding increased at longer delay periods. Conditional probabilities of responding were high shortly after a response, decreased, and then increased to maximum at about 20 sec.

Reward and reward omission: Time-dependent aftereffects in rats and fish

Both goldfish and rats responded faster on a trial following shortly after reward omission than on trials at longer intervals. On trials shortly after a reward, responding was slower than on similar trials presented at longer intervals. These reward omission effects are similar to the invigorating effects of frustrative nonreward.