Observational learning in monkeys

Observer monkeys were housed next to demonstrator monkeys that were conditioned to respond on a multiple reinforcement schedule whose components were fixed-ratio 32, variable-interval 3-min, and extinction 5-min followed by an additional 30 sec of extinction during which every response started a new 30-sec interval. After observational periods from 113 to 210 hr long, during which observers could not perform the response and were given no extrinsic reinforcers, their first-response latencies to fixed ratio and variable interval were as short as the demonstrators; and their rates of responding were well above pre-observational baseline levels. About 8 hr later, a temporal pattern of responding appropriate to the multiple schedule emerged, including non-emission of responses during extinction. Controls lacking the chance to observe did not develop typically patterned responding after 60 hr in one case and, in two other cases, after 80 hr during which, on two occasions, every one of 50 responses was reinforced. In a second experiment, the stimulus lights associated with fixed ratio and variable interval were presented simultaneously. Subjects chose one of the schedules by responding to one of the levers beneath the lights. All subjects initially chose fixed ratio. Seeing the demonstrators switch to variable interval, due to increases in the fixed-ratio requirement, had no effect upon observers, which continued to choose fixed ratio.     

Avoidance response rates during a pre-food stimulus in monkeys

Free-operant avoidance responding was maintained by a shock avoidance schedule in three monkeys. The frequency of avoidance responses during a stimulus terminated by response-independent food pellet presentation was dependent upon the method of pellet delivery. Avoidance rates were relatively increased when food retrieval responses followed pellet delivery. Avoidance rates were decreased when retrieval responses preceded pellet delivery.     

Avoidance learning by Guinea pigs

Albino guinea pigs were trained in shuttle-boxes. Superior performances were achieved with longer CS-US (15 sec. against 5 sec.) and intertrial intervals (90 sec. against 30 sec.). There were no performance increments within sessions, but improvements in performance occurred between sessions. Consolidation mechanisms probably play an important part in avoidance learning by guinea pigs.     

Reversal learning by fornix-transected monkeys

Experiment 1 examined visual reversal learning and in Experiment 2 monkeys were trained to criterion in a serial reversal set between “FR” and “DRO” response requirements. In both cases impairments were observed in fornix-transected monkeys. These results are discussed in connection with previous findings that in serial reversals damage to the hippocampal system in monkeys causes a deficit in spatial but not in visual learning. A unified account is proposed.     

Avoidance learning facilitates temporal processing in the primary auditory cortex

The primary auditory cortex is now known to be involved in learning and memory, as well as auditory perception. For example, spectral tuning often shifts toward or to the frequency of the conditioned stimulus during associative learning. As previous research has focused on tonal frequency, less is known about how learning might alter temporal parameters of response in the auditory cortex. This study addressed the effects of learning on the fidelity of temporal processing. Adult male rats were trained to avoid shock that was signaled by an 8.0 kHz tone. A novel control group received non-contingent tone and shock with shock probability decreasing over days to match the reduced number of shocks received by the avoidance group as they mastered the task. An untrained (nai ve) group served as a baseline. Following training, neuronal responses to white noise and a broad spectrum of tones were determined across the primary auditory cortex in a terminal experiment with subjects under general anesthesia. Avoidance conditioning significantly improved the precision of spike-timing: the coefficient of variation of 1st spike latency was significantly reduced in avoidance animals compared to controls and nai ves, both for tones and for noise. Additionally, avoidance learning was accompanied by a reduction of the latency of peak response, by 2.0-2.5 ms relative to nai ves and approximately 1.0 ms relative to controls. The shock-matched controls also exhibited significantly shorter peak latency of response than nai ves, demonstrating the importance of this non-avoidance control. Plasticity of temporal processing showed no evidence of frequency specificity and developed independently of the non-temporal parameters magnitude of response, frequency tuning and neural threshold, none of which were facilitated. The facilitation of temporal processing suggests that avoidance learning may increase synaptic strength either within the auditory cortex, in the subcortical auditory system, or both.