Poison-enhanced neophobia: Effects of CS-UCSUCS-CS procedures and long-delay training

Experiment 1 (n = 110 male rats) showed that pairing sucrose with toxicosis under forward or backward conditioning procedures yielded reliable poison-enhanced neophobia toward casein hydrolysate. Forward procedures produced reliably greater and more persistent enhancement of neophobia. Experiment 2 (n = 160 male rats) showed that interpolating 10 min, or 1, 4, 8, or 12 hr between sucrose and toxicosis yielded reliable aversion effects to sucrose and poison-enhanced neophobia to casein at each interval except 8 and 12 hr. Generally speaking, the effects of training interval were similar for conditioned aversion and enhanced neophobia but conditioned aversion effects were more enduring.     

Vicious-circle behavior in the Y maze

Laboratory rats were given escape training in both arms of a Y maze followed by extinction in one of four conditions: regular (no shock), punished (both arms containing a shock mid-segment), choice, or forced (one arm containing a shock mid-segment, one arm shock free). Subjects in the punished and forced conditions required more extinction trials than those in the regular extinction condition. The choice condition was intermediate and not significantly different from the others. Choice subjects avoided the shock by choosing the safe alley early and consistently during extinction, but some continued to run for many trials without further punishment. It was suggested that the number of punished trials early in extinction is related to persistence of running, and the results were discussed in relation to the Mowrer-Brown and the discrimination hypotheses.     

Positive contrast obtained in reacquisition following interpolation of nonreinforced or partially reinforced trials

Two experiments investigated the effects of shifting from either nonreinforcement or partial reinforcement (PRF) to continuous reinforcement conditions (CRF). In the first experiment, three groups of rats were given food reinforcement under CRF conditions in a runway followed by regular extinction trials (RE), extinction trials where Ss were delayed for 30 sec before entering the empty goal box (DE), or CRF trials where Ss were delayed for 30 sec before entering the baited goal box (DF). Then all Ss were run on the delayed reinforcement condition (DF). In the final delayed reinforcement condition, group DE ran significantly faster than group DF, reflecting positive contrast. In the second experiment, four groups of rats were trained in a runway to receive either 4% or 18% sucrose reinforcers under either PRF or CRF conditions. Then all Ss were transferred to a Skinner box and bar presses were continuously reinforced, with each S continuing to receive the same sucrose concentration as before. The former PRF Ss, regardless of the reinforcer, bar pressed at a significantly higher rate in the Skinner box than the former CRF Ss. The evidence seemed to favor the view that the effectiveness of a reinforcer is not an absolute, unchanging quantity but rather depends on the historical context in which the reinforcer occurs.     

Infantile stimulation and its effects on frustration- and fear-motivated behavior in rats

Infant rats that were either removed from the nest each day (handled) or left undisturbed (nonhandled) were, in adulthood, given 72 food-reinforced runway acquisition trials followed by 24 trials of extinction training with or without shock. Handled and nonhandled control animals were given runway training without food reinforcement. Reinforced rats ran faster than nonreinforced rats, and handled rats ran faster than nonhandled rats during the initial trials of runway acquisition irrespective of the reinforcement condition. Nonhadled rats stopped running sooner than handled rats when shock was introduced in the goalbox, but differences between handled and nonhandled rats given extinction training without shock were small. Results of a second experiment showed no differences between handled and non-handled rats in the magnitude of the depression effect after an incentive shift. It was concluded that infantile handling had little effect on frustration-motivated behavior, but did affect fear-motivated behavior.     

Stimulus probability and prediction outcome as determinants of choice reaction time: Some procedural considerations

Effects of stimulus probability and prediction outcome on two-choice reaction speed (CRS) were determined when a frequency imbalance was reversed half-way through 300 samples of a 70/30 stimulus distribution and when the same 70/30 distribution was sampled for 1200 trials. Prior to each presentation Ss made a prediction; following each presentation Ss identified the stimulus by pressing a right-hand or left-hand trigger. CRS was faster to correctly predicted stimuli, and faster to the more probable stimulus. Ss who were informed of the frequency imbalance reacted significantly faster than Ss who were not. Both practice and boredom effects were demonstrated by using the extended number of trials. CRS was faster during the second session of 300 trials than during the first; after two sessions, CRS was slower during the second half of two additional sessions.     

Differential runway performance using goal box placement and running trials as discriminative stimuli

Two experiments compared the effects of reinforced, partially reinforced and nonreinforced intertrial goal box placements (ITR, ITP, and ITN respectively) on runway performance. In Experiment I differential responding (animals running slower on nonreinforced (N) trials than on reinforced (R) trials) was observed during acquisition for subjects receiving ITP preceding N trials or subjects receiving ITP before R trials, and also for subjects receiving ITR preceding N trials. No differential responding was observed in subjects receiving ITP prior to both N and R trials or ITN prior to N trials. In extinction, the subjects which had responded differentially during acquisition demonstrated reduced resistance to extinction in comparison to the subjects which had not. In Experiment II, a 2 × 2 factorial design was utilized with placement schedule (ITN and ITP) and type of trial predicted by placement (N and R) serving as the factors. Differential responding was observed in all four groups. The apparent contradiction between the results and the discrimination hypothesis proposed by Capaldi and Olivier (1967) to explain the attenuation of ITR and ITN effects on resistance to extinction is discussed.     

Consummatory Contrast Effects in Nondeprived Rats Following Shifts in Sucrose Concentration

Successive positive and negative contrast effects in consummatory behavior were investigated following shifts in sucrose concentrations in nondeprived subjects. Forty-four male albino rats were given daily 5-min access to either a 4%- or 32%-sucrose solution across a 14-day preshift period. Subjects in each group were then assigned to either a control or shifted condition. Shifted groups were upshifted (4–32%) or downshifted (32–4%) for a 10-day postshift period. Negative contrast was apparent in both lick rate and time spent at the drinking tube across the first 4 days of postshift. Positive contrast effects were not obtained, but rather a significant effect opposite to positive contrast occurred. The improbability of the ceiling effect explanation for the present results is discussed. Differences relative to deprivation state and the role of perceptual (taste) factors in contrast effects are also examined.

     

The role of instrumental responses in memory retrieval in a T-maze

Retrieval of the memory of non-reward on a rewarded trial was investigated here employing rats in a T-maze. A forced choice procedure was used. The daily rewarded (R) and non-rewarded (N) trials always occurred in a fixed order, two R, four N, and finally two R, i.e. the series was R1-R2-N1-N2-N3-N4-R3-R4. In an original acquisition phase, Trial N4 of the series having occurred in a particular spatial alternative, e.g. left, it was followed by R3 either in the same alternative, Groups C and T, or in the opposite alternative, Group R. Group T, unlike Groups C and R, received a relatively long intertrial interval between N4 and R3. In a shift phase, groups were treated as in original acquisition except that the long intertrial interval (Group T) and the change in response (Group R) now occurred between R3 and R4 rather than N4 and R3. The major finding in original acquisition was slower running by Groups T and R than by Group C on Trials N2, N3, and N4. In shift, differences between the groups disappeared. These findings are consistent with the hypothesis that response-produced cues contribute to memory retrieval.     

Prediction outcome and choice reaction time: Inhibition versus facilitation effects

In two-choice RT tasks Ss verbally predicted all stimulus presentations, two-thirds of the presentations, or none of the presentations. Effects of stimulus probability were similar for each type of prediction trial: Correct Prediction Outcome (PO), Incorrect PO, and No-Prediction (NP). When comparisons between Prediction and NP trials were between Ss, reactions on NP trials were significantly faster than reactions POs, but were not slower than reactions to Correct POs. However, when Prediction and NP trials occurred within Ss, reactions on NP trials were not faster than reactions to Incorrect POs, but were significantly slower than reactions to Correct POs. Speculations about Ss' implicit stimulus predictions are offered to interpret differential implications of inhibition and facilitation.     

Peripheral pain enhances the effects of incentive downshifts

Physical pain (induced by tissue damage) and psychological pain (induced by surprising incentive loss) share a set of common neural substrates, but little is known about their interactions. The present research studied such interactions using the formalin test to induce physical pain and consummatory successive negative contrast (cSNC) to induce psychological pain. In the formalin test, animals receive an intradermal injection of formalin (1%) in a hind paw. In cSNC, rats with free access to 32% sucrose show a sharp suppression of drinking behavior after a downshift to 4% sucrose, compared to rats that always receive 4% sucrose. In Experiment 1, formalin administration before the first and second 32-to-4% sucrose downshift trials enhanced cSNC. In Experiment 2, a similar treatment before the first downshift trial after a 16-to-4% sucrose downshift, which normally produces little or no evidence of cSNC, significantly increased cSNC. In Experiment 3, using a 32-to-4% sucrose downshift procedure similar to that of Experiment 1, no effects were observed following formalin administration immediately after Trial 11. Thus, no evidence was found that the effects of physical pain on cSNC were caused by changes in memory consolidation. The procedures used in these experiments offer a new approach to study the neural substrates of interactions between physical and psychological pain.     

Extinction effects following interpolation of instrumental trials among response prevention periods

Two experiments evaluated the effectiveness of response prevention when prevention periods were interpolated with instrumental trials which permitted performance of the originally trained instrumental behavior. In Experiment 1, interpolation of instrumental escape trials under shock and nonshock procedures reliably reduced prevention's influence on performance and yielded extinction responding similar to that of pseudo-prevention controls. In Experiment 2 interpolation of instrumental escape trials under nonshock conditions yielded passive avoidance performance similar to that of pseudo-prevention controls but reliably different from that of a regular prevention group.     

Within-subjects positive and negative contrast effects in rats.

Rats were given alternating 1-min. access periods to 2 tubes containing either 32% or 4% sucrose solutions for daily 6-min. test sessions. Lick rate for 32% was higher under comparison (32 vs. 4) than noncomparison (32 vs. 32) conditions; and lick rate for 4% was lower under comparison conditions (4 vs. 32) than under noncomparison conditions (4 vs. 4). All sucrose conditions were varied within subjects and both positive and negative contrast were obtained with a small n. In addition to lick rate, intake and latency measures also revealed contrast effects. Deprivation conditions altered latency but not lick rate measures of contrast. Reducing the test session to 3 min. (alternating 30-sec. access periods) did not greatly affect contrast. Additional experiments provided evidence for distinct within-days and between-days contrast effects, as well as a between-groups contrast effect.     

Effects of prior exposure on conditioned taste aversion in the rat: androgen- and estrogen-dependent events

The effects of preexposure and gonadal hormone manipulation on the extinction of a conditioned taste aversion were investigated. In Experiment 1, male rats were given one prior exposure to sucrose at some selected time (Days 4, 2, or 1) before a second exposure (Day 0) to sucrose and an LiCl injection. Controls received no prior exposure to sucrose but experienced only the sucrose + LiCl condition (Day 0). under the single exposure condition (Day 0) castrated animals extinguished the aversion faster than either testosterone-treated castrated rats or sham-operated rats. Sham-operated and castrated rats that had received preexposure treatment (Days 4, 2, or 1) were not distinguishable on a within-groups comparison of behavior but differed from their respective controls by exhibiting faster rates of extinction. However, in the testosterone-treated group only the Day 4 preexposure group exhibited a faster extinction rate. In Experiment 2, estradiol, dihydrotestosterone, and testosterone were studied by using only a Day 1 preexposure condition. The testosterone-treated group maintained the aversion for the longest period of time, followed by dihydrotestosterone-treated, sham, castrated, and estradiol-treated groups. It appears that estradiol augments the castration effect whereas dihydrotestosterone attenuates the effect. In Experiment 3, estradiol was administered alone or in combination with two different doses of dihydrotestosterone, and a Day 1 preexposure condition was used. The findings indicate that the outcome of behavior is dependent on the ratio of estradiol to dihydrotestosterone, with variations in this ratio resulting in fast (estrogen effect) to slow (androgen effect) rates of extinction.     

Integration and representation in rats' serial pattern learning in the T-maze

Rats were exposed to three-trial series consisting of reinforced (R) trials and one nonreinforced (N) trial in a fixed order, RRN and RNR (Experiments 1 and 2) or NRR and RRN (Experiment 3), on extended visually distinct runways in a T-maze. When initially presented with the same sequence on each series in a session (separate presentations) with the same runway on all trials within a series (Experiments 1 and 3), all the rats developed slower running speeds on N than on R trials. When a runway was sometimes changed between the first and next two trials during separate presentations training (Experiment 2) or both sequences were later intermixed within each session in each experiment, only rats exposed to each sequence on a specific runway maintained these serial running patterns. Rats displayed serial running patterns on a test RNN sequence similar to that on the RNR sequence (Experiment 2), as would be predicted by an intertrial association model of serial pattern learning (Capaldi & Molina, 1979), but responded on test RRR and NRN sequences (Experiment 3) as would be predicted by an ordinal-trial-tag/intratrial association model (Burns, Wiley, & Payne, 1986). Results from test series of free-choice trials in Experiments 1 and 2 failed to support a prediction of the intratrial association model that these rats would integrate RRN and RNR sequences. Rather than always selecting a baited runway on both the second and the third free-choice trials, the rats only selected a baited runway on the third trial on the basis of their choice on the second trial, as would be predicted by the intertrial association model. Only after experiencing all possible outcome sequences during forced-choice training in Experiment 3 did these rats predominantly select a baited runway on every free-choice trial.     

Semantic priming and retrieval from lexical memory: Evidence for facilitatory and inhibitory processes

Immediately prior to each visually presented target letter string to which the subject made a speeded word-nonword classification response, a visually presented prime to which no overt response was required was shown for 360, 600, or 2,000 msec. For word (W) target trials, the priming event was either a semantically neutral warning signal (Condition NX), a word semantically related to the target word (Condition R), or a word semantically unrelated to the target word (Condition U); for nonword (N) target trials, the priming event was either the neutral warning signal (Condition NX) or a word prime (Condition WP). For the W target trials, reaction times (RTs) were slower in Condition U than in Condition NX and equally so for all three prime durations; RTs were faster in Condition R than in Condition NX and to a greater degree for the 600- and 2,000-msec prime durations than for the 360-msec prime duration. For the N targets, RTs were faster in Condition WP than in Condition NX and equally so for all prime durations. These results were interpreted within the framework of a two-factor theory of attention proposed by Posner and Snyder (1975a).     

Organized responding in instrumental learning: Chunks and superchunks

Two investigations attempted to determine if rats could learn that the second series of runway trials, the test series, was the same as the first series, the study series. Series were constructed from runway responses which terminated either in food reward (R) or nonreward (N). In the series RNR, for example, three successive responses terminated in R, N, and R, respectively. Rats manifested mastery of a series by running fast to R and slow to N. In Experiment 1 the test series (either RNR or RNN) occurred in a black runway about 15 s after the study series presented in a white runway. In Experiment 2 the test series (either RN or RRN) occurred in a gray runway about 15 min after the study series, also in a gray runway. In both experiments rats learned that the study series was the same as the test series. A hierarchical interpretation was suggested in which runway trials are organized into series, series being organized into lists.     

Representation of serial order in pigeons (Columba livia)

In Experiment 1, 2 groups of pigeons were trained to respond to either a 4-item (A→B→C→D) or 5-item (A→B→C→D→E) list. After learning their respective list, half of the subjects were trained on a positive pair with reinforcement provided when pairs were responded to in the order true to that of the original sequence (4-item: B→C; 5-item: B→D). The remaining subjects were trained on a negative pair with reinforcement provided for responding to the pairs in the order opposite to that learned in the original sequence (4-item: C→B; 5-item: D→B). Subjects in the positive pair condition learned their respective pair faster than did subjects in the negative pair condition. In Experiment 2, after reaching criterion on a 4-item list, subjects received 16 BC probe trials spread across 4 sessions of training. Subjects performed significantly above chance on the probe trials. The performance of our subjects in Experiments 1 and 2 demonstrates that, similar to monkeys, pigeons form a representation of the lists that they learn.     

Response patterning in goldfish: single alternation in a Pavlovian aversive paradigm

Single alternation behavior was studied in a Pavlovian aversive shuttle-response situation using goldfish. Independent groups of fish were given either a fixed interval between alternating reinforced (R) and nonreinforced (N) trials or were given differential temporal information between trials. Although all groups exhibited higher response probabilities on reinforced than on nonreinforced trials, goldfish receiving a short interval (10 s) following R trials and a long interval (60 s) following N trials (R10N60) demonstrated significantly superior alternation performance compared with subjects receiving a fixed intertrial interval (R35N35) or a long interval following R trials and a short interval following N trials (R60N10). The alternation performance exhibited by the R10N60 group was shown to be equivalent to that of subjects receiving standard color discrimination training. However, the alternation performance in group R35N35 showed a great deal of within-subject variability and raises questions concerning the elusive nature of alternation using Pavlovian conditioning procedures.     

Apparent Incentive Contrast Effects in Autoshaping with Rats

The effects of shifts in reward quality and quantity on Pavlovian acquisition were studied in rats. In Experiment 1, animals preexposed to unsignaled food pellets, 10% sucrose solution, or home cage controls subsequently received autoshaping training (response-independent lever-pellet or lever-solution pairings, in three groups each). Unsignaled preexposure to sucrose solution facilitated autoshaping for pellets (relative to unshifted controls), whereas unsignaled preexposure to pellets retarded autoshaping for sucrose solution. In Experiment 2, unsignaled preexposure to 30% sucrose solution impaired acquisition reinforced by food pellets, relative to 2% solution. Using a choice procedure, Experiment 3 demonstrated that rats prefer pellets to either 2 or 10% sucrose solutions, but they prefer the 30% solution to the pellets. Experiment 4 demonstrated the facilitatory effect after an upward shift in reward magnitude rather than quality (from 1 to 12 pellets), but provided weaker evidence for retardation following a downward magnitude shift. Experiment 5 was similar to Experiment 4, except that animals received autoshaping training from the outset. No evidence of successive positive contrast was obtained, but there was a significant successive negative contrast effect. Moreover, extinction was faster after acquisition with 12 pellets rather than 1. These results suggest the presence of incentive contrast effects under Pavlovian training conditions.     

Effect of an audience on learning a novel motor skill

The purpose of this study was to assess effects of an audience on learning a novel motor skill. Subjects (N=64) were randomly assigned to one of four experimental conditions and administered 15 30-sec. trials with 30 sec. intertrial periods on a pursuit rotor task on two different days. Comparison of Time-on Target performance between conditions indicated that the No Audience condition had significantly higher performance than the Audience condition in Session 1. Comparison of Absolute Retention and Final Retention scores among the four experimental conditions in Session 2 after 48 hr. yielded no significant differences attributable to the presence of an audience, thus supporting the hypothesis that an audience would have no effect on learning.