Ontogeny of long-term,nonassociative memory in the rat

The primary purpose of the present study was to assess the ontogeny of nonassociative learning and memory in 16-, 30-, and 75-day-old rats. In each of three experiments, habituation of the orienting response to a novel auditory stimulus was measured. The orienting response is an unconditioned reaction elicited by innocuous environmental stimulation that habituates with repeated stimulus presentations. Both an autonomic component (heart-rate deceleration) and a behavioral index (head jerk) of the orienting response were recorded in this study. Although no age differences in rate of habituation (i.e., rate of nonassociative learning) were found (see Experiment 1), a marked effect of age on retention of habituation was observed. Preweanling rats retained habituation of the orienting response to an auditory stimulus for less than 4 h (Experiment 2), whereas adult animals exhibited no forgetting even after a 1-week interval (Experiment 3). These results are discussed in terms of (1) demonstrations of age-related differences in associative memory, (2) the persistence of nonassociative memories in adults, and (3) the significance of the orienting response as a measure of retention of nonassociative learning.     

Differential effects of a retention interval on latent inhibition and the habituation of an orienting response

In Experiment 1, rats experienced presentations of a discrete visual stimulus (Stage 1) until habituation of the orienting response (OR) occurred. On a test session given after an interval of 16 days (Stage 2) the OR reappeared. For control subjects that received no Stage 1 training but presentations of the light in Stage 2, habituation persisted during the test. All subjects then received conditioning trials on which the light preceded the delivery of food. They showed latent inhibition, acquiring the conditioned response less readily than control subjects that had not previously experienced the light. Experiment 2 confirmed that the latent inhibition effect survived the retention interval for subjects that received no habituation test session. This pattern of results implies that habituation of the OR and latent inhibition are determined by different mechanisms.     

Effect of number of trials,interstimulus interval,and dishabituation during CS habituation on subsequent conditioning in a CER paradigm

Three experiments were conducted to investigate the influence of variables during habituation of a CS on a subsequent conditioning to that CS in a conditioned emotional response paradigm. Experiment I varied the number of habituation trials received before conditioning, and it was found that additional habituation trials resulted in a further attenuation of conditioning. Experiment II varied the interstimulus interval of the habituating stimulus, and it was found that the longer intervals produced the greater attenuation in conditioning. Experiment III examined the effect of interpolating another stimulus between habituation and conditioning (dishabituation), and it was found that the dishabituating stimulus augmented subsequent conditioning. It was concluded that manipulations during habituation training that produce the greatest decrement in response to a stimulus, when assessed under equivalent conditions for all animals, have the greatest attenuating effect on subsequent conditioning to that stimulus.     

A Pavlovian analysis of food-attraction conditioning in the snailHelix aspersa

Following brief pairing of an odor with a feeding experience (food-attraction conditioning), snails will lower their tentacles when subsequently presented with that odor alone. Three experiments investigated the possible behavioral mechanism mediating food-attraction conditioning in the snailHelix aspersa. It is suggested that food-attraction conditioning is an example of Pavlovian conditioning. In this case, the odor (conditioned stimulus) is paired with oral stimulation (unconditioned stimulus), which elicits lowering of the tentacles (unconditioned response). Following conditioning, the odor comes to elicit lowering of the tentacles (conditioned response). Experiment 1 ruled out nonassociative effects, such as habituation and sensitization, using an unpaired control group. Experiment 2 provided further evidence against a role for habituation of neophobia, through the demonstration of extinction following conditioning. In Experiment 3, an omission procedure was used to rule out the possible role of instrumental contingencies.     

Latent habituation of the orienting response in the preweanling rat

The effect of inhibiting the orienting response on information processing was examined in four experiments. A nonsignal auditory stimulus was presented four times to preweanhng rats either 30 sec or 15 min after they had been placed in an unfamiliar environment (Experiments 1A and 2), shocked (Experiment 1B)5 or experienced a shift in environmental context (Experiment 1C). Both an autonomic (heart rate) and a behavioral componentx of the orienting response to the novel stimulus were recorded. In the 15-min condition, the auditory stimulus elicited a consistent orienting response on the first trial that habituated rapidly with successive trials. In contrast, the auditory stimulus did not elicit a detectable orienting response in the 30-sec condition on any of the four trials. However, when the auditory stimulus was re-presented after a brief retention interval, a comparable level of habituation was seen in both groups. These results demonstrate that animals in the 30-sec condition detected, attended to, and encoded the auditory stimulus even though they did not orient, either autonomically or behaviorally, to that stimulus when it was first presented. This process of response-independent habituation is best described as latent habituation. Like latent learning, latent habituation took place in the absence of any observable change in behavior. The implications of this effect for current theories of habituation and of the orienting response are discussed.     

Habituation and recovery of orienting in rats as a function of stimulus significance

Three experiments measured orienting of rats to stimuli varying in intrinsic significance. In the first, rats showed greater reactivity to a recording of a conspecific’s distress squeal than to a simulated mimic squeal when the stimuli were presented at 100 dB but not at 80 dB, and orienting to all stimuli habituated rapidly with repeated stimulus exposures. Experiment 2 showed that, following several stimulus exposures, recovery of orienting after rest periods of 1 and 7 days was a function of the stimulus: Orienting to the distress squeal presented at 100 dB recovered more rapidly than did orienting to the mimic squeal at 100 dB or to either the mimic or the distress squeal presented at 80 dB. Experiment 3 showed that habituation to the most significant stimulus, the distress squeal presented at 100 dB, was retarded at long (24-h) interstimulus intervals, presumably a consequence of less stimulus-to-stimulus transfer of habituation with this stimulus. The results are discussed in terms of biological constraints on habituation of orienting and on recovery of orienting following habituation.     

The psychophysics of remembered duration

Pigeons were trained on a psychophysical choice task to make one response after a 2-sec signal and a different response after a 10-sec signal. Delayed dimensional control was assessed by presenting durations intermediate to the short and long signals and by introducing delays between the signals and choice opportunities. In Experiment 1, choices after intermediate durations were not reinforced; in Experiment 2, one choice was reinforced after the three shortest durations and another was reinforced after the three longest durations. In Experiment 1, the slopes of the psychophysical functions decreased with increases in delays, but the decrease in stimulus control was not unbiased; choice probabilities decreased for longer durations, but did not increase for shorter durations. Experiment 2 revealed the same generalized loss of stimulus control on the temporal dimension, but not the same pattern of bias; temporal control was relinquished equally for shorter and longer durations. These results are evaluated in the context of the subjective shortening model of remembered duration (Spetch & Wilkie, 1983) and Staddon’s theory of timing and remembering (Staddon, 1984).     

The effect of a retention interval on habituation of the neophobic response

In three experiments, water-deprived rats were preexposed to a novel saccharin solution. The neophobic response to this flavor was then assessed in a choice test involving saccharin and water, administered either immediately or 24 h after preexposure. Subjects displayed a significantly greater preference for saccharin at the 24-h test than at the immediate test (Experiments 2 and 3). This “incubation” effect was eliminated if the subjects were more water-deprived at the delayed test than at the immediate test (Experiment 1), and enhanced if the amount of saccharin consumed during preexposure was increased (Experiment 3). Possible ways in which current theories of habituation might be amended in order to accommodate this finding are discussed.     

Roles of visual and taste cues in ingestional neophobia: Response latency effects in chicks (Gallus domesticus)

Latency measures of starting to drink and of consummatory behavior were used to investigate ingestional neophobia to novel visual and novel taste cues in chicks. In Experiment 1 (N = 36), latencies to start drinking were reliably shorter to ingesta that appeared familiar from previous rearing or preexposure procedures. After drinking started, consummatory responding occurred reliably more rapidly to familiar taste cues than to novel ones. However, the presence of familiar visual cues reliably facilitated consumption of a novel taste. Experiments 2 and 3 (Ns = 144 and 180) were performed to evaluate, respectively, whether the ingestional effects of taste stimulus intensity, 0%–6% vinegar, and of visual stimulus intensity, 0%–1.0% concentrations of red food-coloring in water, changed during ontogeny for chicks 3, 5, and 7 days old. In Experiment 2, reliable direct effects of taste concentration on consummatory response latencies occurred immediately in 7-day-olds but were delayed in 3-day-olds. In Experiment 3, each age group immediately showed reliably slower starting and consummatory response times, the higher the concentration of red food-coloring. Intake performance in both experiments was consistent with the latency data. Experiments 1–3 showed that visual and taste cues of ingesta separately influenced approach and consummatory behaviors of the ingestive response sequence and that these influences depend on ontogenetic events.     

Interval between preexposure and test determines the magnitude of latent inhibition: Implications for an interference account

The effect of a retention interval on latent inhibition was studied in three experiments by using rats and the conditioned taste-aversion procedure. In Experiment 1, we demonstrated an apparent loss of latent inhibition (i.e., a strengthening of the aversion) in preexposed subjects that experienced a retention interval of 12 days between conditioning and the test. In Experiment 2, we found no effect of this retention interval on the habituation of neophobia produced by the phase of exposure to the flavor. In Experiment 3, we showed that interposing a retention interval between preexposure and conditioning produced effects exactly comparable to those seen in Experiment 1. The implications of these results for rival theories of latent inhibition, as an acquisition deficit or as a case of interference at retrieval, are discussed.     

Persistent effect of noise on the acoustic startle reflex in the rat

Continuous noise facilitates acoustic startle reflexes in the rat. Rats were exposed to noise for 23 h (Experiment 1) or to 23 h of startle eliciting stimuli at the rate of 1/min (Experiment 2). Facilitation was reduced following habituation in Experiment 2, but was unaffected by prolonged noise exposure in Experiment 1. Reflex inhibition produced by a brief noise was not altered by habituation. Prior experiments show that increases in intensity of continuous noise engage two disparate processes which affect the acoustic startle reflex, one facilitatory (arousal) and one inhibitory (masking). The present data reveal that arousal is not diminished by prolonged noise exposure. The loss of facilitation following reflex habituation may be attributed to its increased susceptibility to masking, or to a direct effect of stimulus repetition on the arousal process normally associated with the noise background.     

Effects of distractor familiarity on habituation of neophobia

When the first presentation of a neophobic flavor is immediately followed by a distractor flavor, habituation of the neophobic response is typically attenuated. This is manifested by the fact that neophobia is still shown to the target flavor on its second presentation. Three experiments investigated the prediction that this effect will occur only for novel, but not familiar, distractor solutions. Experiments 1 and 2 found that, contrary to this prediction, both novel and familiar distractors can attenuate the habituation of a neophobic response. In Experiment 3, however, when the distractor was made very much more familiar, it lost its ability to interfere with the habituation of neophobia to the target solution. These results are discussed in terms of Wagner’s (1981) theory of habituation.     

The effect of drug habituation before and after taste aversion learning in rats

In Experiment I, rats received eight habituation injections of either lithium chloride (LiCl) or sodium chloride (NaCl), then two aversion training trials in which access to saccharin solution was followed by LiCl injections, and finally eight extinction trials with saccharin but no injections. The rats habituated to LiCl showed less aversion to saccharin during training and extinction. In Experiment II, rats received two aversion training trials, then eight habituation trials to either LiCl or NaCl, then eight extinction trials, four more aversion training trials, and eight more extinction trials. The rats habituated to LiCl did not differ during the first extinction period from those habituated to NaCl, but showed less aversion to saccharin during the second training and extinction periods. Consequently, habituation to LiCl reduces the learning of an aversion to saccharin but does not reduce the performance of a previously learned aversion.     

Inhibition of exploratory behavior in the rat by handling

The effect of tail-handling on exploratory behavior of the rat, measured as step-through latency in a well-lighted, two-box apparatus, was investigated. Male adult Wistar rats, aged 60 days, were employed in all three experiments. Experiment 1, in which the subjects were handled at different times after entering the goal chamber (0, 10, 30, 60, 300, and 600 sec), showed that immediate handling, relative to detention in the goal chamber (delay of handling) had an inhibitory effect on exploration. Experiment 2 showed that groups handled immediately after entering the goal chamber but then detained there for different durations all showed the same progressive inhibition of exploration. Experiment 3 showed that the inhibition of exploration (very long step-through latencies) due to tail-handling immediately after entering the goal chamber could be significantly decreased by further trials in which handling was delayed for a sufficient duration (30 sec or more). Handling is discussed as a stimulus that is aversive enough to elicit conditioned passive-avoidance responses (inhibition of exploratory behavior), although it is subject to rapid extinction.     

Habituation of two response systems in the lizard,Anolis carolinensis

These experiments investigated habituation of two responses in the lizardAnolis carolinensis. In Experiment 1, intertrial intervals (ITI) of 5, 30, and 120 sec had various effects on habituation of dewlap distension and optokinetic response (OKR). Although there were no size differences noted for the OKR, smaller anoles (50–58 mm snout-vent length, SVL) failed to habituate under the 30- and 120-sec ITI of the dewlap response, while larger anoles (? 59-mm SVL) habituated under each ITI tested, with no response level differences between ITIs. Rates of habituation were similar within and across responses. In a second experiment, larger anoles were employed to study recovery and retention of dewlap distension and OKR habituation after 15-min and 24-h intervals. Complete recovery of both responses occurred in 24 h, with substantial recovery of both responses after 15 min. Retention was present for both responses after 15 min but not after 24 h. A multiple response-system approach is offered as a promising method for research and theories in habituation. Rather than concentrating upon a single response in one or more species, a multiple response-system approach examines similarities and differences in the habituation of various responses within a single species.     

“Why Does Rain Fall?”: Children Prefer to Learn From an Informant Who Uses Noncircular Explanations

These two studies explored 3‐ and 5‐year‐olds' evaluation of noncircular and circular explanations, and their use of such explanations to determine informant credibility. Although 5‐year‐olds demonstrated a selective preference for noncircular over circular explanations (Experiment 1: Long Explanations; Experiment 2: Short Explanations), 3‐year‐olds only demonstrated a preference for the noncircular when the explanations were shortened (Experiment 2). Children's evaluation of the explanations extended to their inferences about the informants' future credibility. Both age groups demonstrated a selective preference for learning novel explanations from an informant who had previously provided noncircular explanations—although only 5‐year‐olds also preferred to learn novel labels from her. The implications and scope of children's ability to monitor the quality of an informant's explanation are discussed.     

Pigeons’ memory for event duration: Differences between visual and auditory signals

In Experiment 1, pigeons were trained to discriminate short (2 sec) and long (8 sec) durations of tone by responding to red and green comparison stimuli. During delay testing, a systematic response bias to the comparison stimulus correct for the long duration occurred. Tests of responding without the tone reduced accuracy on long-sample trials but not on short-sample trials suggesting that the pigeons were attending to the tone and not simply timing the total trial duration. The pigeons were then trained to match short (2 sec) and long (8 sec) durations of light to blue/yellow comparisons. During delay testing, “choose-long errors” occurred following tone durations, but “choose-short errors” occurred following light durations. In Experiment 2, accuracy was assessed on test trials in which the tone and the light signals were simultaneously presented for the same duration or for different durations. Pigeons responded accurately to durations of light, but were unable to accurately respond to durations of tone simultaneously presented with the light. The data from Experiment 1 suggest that there are important differences between light and tone signals with respect to the events that control the termination of timing. The data from Experiment 2 indicate that pigeons cannot simultaneously time visual and auditory signals independently and without interference. Consequently, they are inconsistent with the idea that there is a single internal clock that times both tone and light durations.     

Timing in retroactive interference

Retroactive interference is conventionally viewed as attenuated retrieval of a target association due to the training of a second association between training and testing of the target association. In three experiments in which water-deprived rats were used as subjects, we manipulated the durations of the time between cue termination and outcome onset (Experiment 1), the durations of the target and the interfering cues (Experiment 2), and the durations of the outcome used during target and interfering training (Experiment 3). Greater interference was consistently observed between associations bearing a high degree of similarity in their temporal structure, which suggests that interference occurs between complex representations that encode not only the physical attributes of the stimuli, but also their temporal characteristics.     

The role of habituation of the response to LiCl in the US-preexposure effect

In two experiments, rats received preexposure consisting of six intraperitoneal injections of lithium chloride (LiCl). This treatment reduced the magnitude of the unconditioned response (UR; suppressed consumption of a novel flavor) evoked by an additional injection (Experiment 1) or by oral consumption (Experiment 2) of LiCl. In both experiments, preexposure also attenuated the acquisition of a conditioned aversion with an LiCl injection as the unconditioned stimulus (US) but had no effect on the aversion produced when the US was oral consumption of LiCl (Experiment 2). These results are consistent with the view that the reduced ability of the preexposed US to serve as a reinforcer depends on blocking by injection-related cues and is independent of habituation of the UR recorded in the present study. Possible interpretations of this dissociation are discussed.     

Concurrent schedules of wheel-running reinforcement: Choice between different durations of opportunity to run in rats

How do animals choose between opportunities to run of different durations? Are longer durations preferred over shorter durations because they permit a greater number of revolutions? Are shorter durations preferred because they engender higher rates of running? Will longer durations be chosen because running is less constrained? The present study reports on three experiments that attempted to address these questions. In the first experiment, five male Wistar rats chose between 10-sec and 50-sec opportunities to run on modified concurrent variable-interval (VI) schedules. Across conditions, the durations associated with the alternatives were reversed. Response, time, and reinforcer proportions did not vary from indifference. In a second experiment, eight female Long-Evans rats chose between opportunities to run of equal (30 sec) and unequal durations (10 sec and 50 sec) on concurrent variable-ratio (VR) schedules. As in Experiment 1, between presentations of equal duration conditions, 10-sec and 50-sec durations were reversed. Results showed that response, time, and reinforcer proportions on an alternative did not vary with reinforcer duration. In a third experiment, using concurrent VR schedules, durations were systematically varied to decrease the shorter duration toward 0 sec. As the shorter duration decreased, response, time, and reinforcer proportions shifted toward the longer duration. In summary, differences in durations of opportunities to run did not affect choice behavior in a manner consistent with the assumption that a longer reinforcer is a larger reinforcer.