Ontogeny of thermoregulatory mechanisms in the rat.

The ability of rats to select a warm environment was studied as a function of postnatal age (birth to 13 days). Animals younger than 5 days demonstrated no choice response (movement to a warm compartment, 36-37 degrees C); however, they did demonstrate movement within the start compartment (23 degrees C). Increasing the motor capabilities of the pups, by injection of L-3,4 dihydroxyphenylalanine (L-dopa, 50 mg/kg), elicited a choice response in 4-5 day-old animals. Younger animals demonstrated no choice of a warm environment even though they moved considerably. Also there was no difference between L-dopa-treated and control animals in the magnitude of temperature change in pups isolated from their mother for 1 hr. The evidence suggests development of behavioral thermoregulatory mechanisms prior to abilities for internal regulation.     

Reinforcement rate and force proportional reinforcement

The research examines the consequences of making two reinforcement contingencies simultaneously available for the same bar-pressing response. Specifically, two experiments are described which concern the effects of reinforcement rate upon force proportional reinforcement (FPR). In Experiment 1, reinforcement rate was constrained by combining differential reinforcement of low rate with a force-proportional reinforcement contingency. The group of rats exposed to this regimen eventually showed a significant increase in response force compared to control groups. Experimental vs control response rates were not significantly different. In Experiment 2, reinforcement rate was affected through the expedient of relating the probability of obtaining a single pellet to the response force. The group for which the probability-force relationship was discontinuous came to exert higher forces than either a group for which the relationship was fairly continuous or an ordinary variable ratio control group. Response rate was significantly higher for the control group.     

Transfer of the signaling properties of aversive CSs to an instrumental appetitive discrimination

Rats received Pavlovian conditioning in which, based on a shock US, white noise was established for different groups as an aversive CS+, CSo, or CS?. Then, half of each group received the CS contingent upon either the food-reinforced or nonreinforced response in an easy, choice discrimination. Correct responses, i.e., number of reinforcements, to criterion showed that a CS+ for the reinforced response facilitated learning, whereas a CS? retarded learning; conversely, a CS+ for the nonreinforced response retarded learning, whereas a CS? facilitated learning. The same contingency difference occurred with errors to criterion for CS? subjects but was obscured for CS+ subjects apparently by an avoidance-producing effect of the CS+. In support of the generality of the transfer effect, Z-score transforms of the correct-response data showed that the magnitude of transfer was comparable to that obtained in more difficult discriminations. Collectively, the findings indicate that an aversive CS can function as a transformed signal for the presence (CS+) or absence (CS?) of an appetitive reinforcer and that the signal's control of behavior is via a within-chain mediational process.     

Phonetic recoding and reading difficulty in beginning readers

The results of a recent study (Liberman, Shankweiler, Liberman, Fowler, & Fischer, 1977) suggest that good beginning readers are more affected than poor readers by the phonetic characteristics of visually presented items in a recall task. The good readers made significantly more recall errors on strings of letters with rhyming letter names than on nonrhyming sequences; in contrast, the poor readers made roughly equal numbers of errors on the rhyming and nonrhyming letter strings. The purpose of the present study was to determine whether the interaction between reading ability and phonetic similarity is solely determined by different rehearsal strategies of the two groups. Accordingly, good and poor readers were tested on rhyming and nonrhyming words using a recognition memory paradigm that minimized the opportunity for rehearsal. Performance of the good readers was more affected by phonetic similarity than that of the poor readers, in agreement with the earlier study. The present findings support the hypothesis that good and poor readers do differ in their ability to access a phonetic representation.     

Hardware techniques for analog processing using the State Systems PDP-8 I/O interface

Methods are described for construction and use of an analog-to-digital (A/D) converter system which is interfaced with a PDP-8/E through the State Systems interface. Eight bits of one input word are used to bring the results of A/D conversion into the accumulator, and four bits of an output word supply convert and channel-select pulses for the A/D converter and associated eight-channel multiplexer. With a Datei ADC-EH8B1 A/D converter, which digitizes a sample in 4.0 microsec, the system software can perform a conversion in 18.8 microsec. Approximate cost of parts for fabricating the hardware is about $120. Examples of software incorporating the A/D capability are presented for a laboratory computer system used to measure operant response force.     

A model of memory in concept learning

A concept learning model was developed and tested in two conjunctive attribute identification tasks. The model includes assumptions about the focus of attention, decision making, and memory for stimulus information and prior decisions. Predictions are made about how S changes his hypothesis following an error. Procedures in both tasks allowed inference of the subject's current hypothesis. The hypothesis selections and error statistics were in the majority of cases accurately predicted by the model. Deviations from predictions on hypothesis sampling occurred for naive Ss but not for trained Ss who were required to state a hypothesis on each trial.     

Changes in pain reactivity induced by unconditioned and conditioned excitatory and inhibitory stimuli

In three experiments we investigated the effects of aversive-conditioning components on the reactivity of rats to pain. After training in Experiment 1 with a discrete conditioned stimulus (CS) for a shock unconditioned stimulus (US), different groups were exposed to the CS, US, CS/Us compound, just the training context, or none of those immediately prior to a hot-plate test assessing the latency of a paw-lick response. Relative to no exposure and context alone, the CS produced a shorter latency--that is, an apparent sensitization effect--whereas the US produced a longer latency--that is, a hypoalgesic effect--that was actually augmented by the CS/US compound. Furthermore, whereas the US-induced hypoalgesia was unaffected by the opiate antagonist, naloxone, hypoalgesia produced by the CS/US compound was appreciably decremented by the drug. Experiment 2 showed the same effects with parameters more typical of conditioning research. Experiment 3 compared signals for the presence (CS+) and absence (CS-) of the US. The CS- did not itself affect pain reactivity, but in inhibited the effects of the CS+, US, and CS+/US compound. Collectively, the results suggest that a CS+sensitizes the animal to imminent events and also potentiates an opioid reaction that supplants the less effective nonopioid hypoalgesia induced by the US. In contrast, a CS- functions as a general moderator of excitation, inhibiting both sensitization and hypoalgesic effects, whether opioid or nonopioid.