Blocked and test-stimulus exposure effects in perceptual learning re-examined

Three experiments re-examined the effects of blocked or alternated exposure to the conditioning and test stimuli and the effect of simple exposure to the test stimulus, on stimulus generalization. In all experiments rats received conditioning where a compound flavor, AX, was paired with LiCl-induced illness. All rats were tested for generalization with another flavor, BX. In Experiment 1, rats that received alternating exposure to the two flavor compounds, AX and BX, prior to conditioning showed less generalization to BX than rats that received no exposure. Exposure to BX or AX alone was also somewhat effective in reducing generalization. In Experiment 2 blocked exposure to AX and BX prior to conditioning was effective in reducing generalization, as was alternated exposure, and extended exposure to BX was more effective than the other procedures. In Experiment 3, exposure to X alone prior to conditioning produced generalization equal to that produced by alternated or blocked exposure and replicated the effect of extended exposure to BX found in the previous experiment. The relevance of the results to the theories proposed by McLaren and Macintosh [Anim. Learn. Behav. 28 (2000) 211] and Hall [Q. J. Exp. Psychol. B 56 (2003) 43] is discussed.     

The contribution of latent inhibition to reduced generalization after pre-exposure to the test stimulus

Two experiments assessed the contribution of latent inhibition to the generalization-reducing effects of pre-exposure to the test stimulus using a taste aversion procedure in rats. In both experiments, lithium chloride induced illness was paired with a flavor compound (AX) of either salt or sugar (A or B) and hydrochloric acid (X). Generalization of the resulting aversion to a test compound (BX), was assessed after varying pre-exposure to BX, X, and B. Experiment 1 showed that generalization to BX was less when BX itself had been exposed than equivalent pre-exposure to either B and X separately or to B and a new compound (CX). Experiment 2 showed that levels of generalization varied directly as a function of the amount of pre-exposure to BX. The findings show that latent inhibition alone cannot account for the generalization-reducing effect of pre-exposure to BX.     

Salience modulation and associative inhibition interaction: Short but not long exposure to similar stimuli protects the salience of the unique elements

In three experiments, rats were given preexposure to two similar flavour compounds, AX and BX. Following preexposure, conditioning trials took place in which AX was paired with an illness-induced unconditioned stimulus. Animals that were given short alternated preexposure to AX and BX, showed higher generalization of conditioned aversion to AX to a new compound, AN, than animals that were given blocked preexposure (short and long) and long alternated preexposure (Experiments 1 and 2); and showed less preference for A when they were given a choice between A and X (Experiment 3). These results have been taken to indicate that the salience of the A element is well preserved after short alternated preexposure, but declines when preexposure goes on for some more trials. The results reported support the notion that perceptual learning is a multi-determined phenomenon that depends on salience modulation processes after relatively short preexposure, and on an associative inhibition mechanism after prolonged preexposure.     

Dissociation between the Espinet and perceptual learning effects in flavour aversion conditioning

In three experiments rats were given pre-exposure to two compound flavours, AX and BX, the two compounds being presented for some subjects on alternate trials (the intermixed schedule) and, for others, in separate blocks of trials (the blocked schedule). After aversion conditioning with A (in Experiments 1 and 2), the inhibitory properties of B were tested using both retardation (Experiment 1) and summation tests (Experiment 2). The results failed to support the proposal [Anim. Learn. Behav. 23 (1995) 361] that B should acquire inhibitory properties in the intermixed condition (the "Espinet effect"). Experiment 3 demonstrated that generalisation to BX after conditioning with AX was attenuated by intermixed pre-exposure (a perceptual learning effect). This pattern of results challenges the hypothesis that inhibitory learning during intermixed pre-exposure to AX and BX can account for both the Espinet and the perceptual learning effects.     

Order effects after blocked preexposure to two compound flavors

In the first three experiments two groups of rats received prolonged blocked preexposure to AX–BX or to BX–AX. Experiment 1 showed that conditioning of AX after preexposure resulted in less generalization to BX in the AX–BX group than in the BX–AX group. Experiments 2 and 3 constituted, respectively, retardation and summation tests of the inhibitory properties acquired by B after preexposure and conditioning of A. Excitatory conditioning of B was retarded in the AX–BX group (Experiment 2) and only in this group B was able to alleviate the aversion conditioned to a new stimulus (Experiment 3). These results are explained as a consequence of the formation, in the AX–BX group, of inhibitory associations directed from B to A. A fourth experiment provided evidence that the A ↔ X association was preserved until the end of the preexposure phase in this group, which is a requisite for the formation of these inhibitory associations.     

Distractor effects upon habituation of complex stimuli

In two experiments, rats were given serial forward (the target followed by the distractor) or backward (the distractor followed by the target) exposure to two compound flavor stimuli that could be either similar (Salt-X/AX) or dissimilar (Salt-X/AY, Experiment 1; Salt/AX, Experiment 2). Following pre-exposure, the Salt element was presented in a compound with a novel flavor, N. The salience or effectiveness of the Salt element was then assessed by presenting the new flavor, N, under a state of salt appetite. Experiments 1 and 2 revealed that the order of presentation modulated the habituation of the Salt element only when the distractor was similar to the target: the Salt element was more salient after forward than backward pre-exposure. In the groups Dissimilar the order of pre-exposure was irrelevant; however, when the Salt element was presented in compound with a second element (Salt-X, Experiment 1), its salience was preserved, whereas when it was presented alone (Salt, Experiment 2) its salience was significantly reduced. These results, which are discussed in terms of Wagner (1981) theory of habituation, inform about the way in which stimuli presented closely in time are processed.     

An examination of the effectiveness of inflation and deflation treatments in detecting within-compound learning of a taste aversion

Two conditioned taste aversion experiments with rats assessed the relative effectiveness in providing evidence of within-compound learning of different procedures that involve the initial compound presentation of two stimuli, A and X, with the unconditioned stimulus (i.e., AX+). In Experiment 1, following a single AX+ trial, groups A+ and B+ received an additional conditioning trial (i.e., inflation treatment) with A and B, respectively, whereas group A- received an extinction trial (i.e., deflation treatment) with A. The results showed a reduction in the aversion elicited by the target stimulus, X, in group A- relative to both groups A+ and B+, which did not differ. Experiment 2 further investigated the failure of group A+ to increase the aversion to X relative to control group B+ by pairing A or B with either the same unconditioned stimulus that was previously paired with AX (groups A+ and B+) or with a stronger unconditioned stimulus (groups A* and B*). The results showed increased aversion to X in group A* relative to group B*, but not in group A+ relative to group B+. These results are interpreted as indicative of extinction of the within-compound association during the treatment with A, which could likely impair the detection of within-compound learning following an inflation, but not a deflation treatment.     

The effects of cue competition on timing in pigeons

We studied the effects of cue competition on timing in both overshadowing and blocking operant procedures with pigeons. A white center key delivered reward when pecked 30 s after a red or green sidekey was presented and 10 s after presentation of the alternate color on the other sidekey. In Experiment 1, key presentations were concurrent during training trials for overshadow-condition pigeons, while side key presentations were separated across training trials for control birds. In Experiment 2, half of the birds (Blocking group) were given pre-exposure trials to either the 10-s or 30-s sidekey condition. Both blocking-condition and control birds were then given trials of concurrent side key presentations. Peak time curves were compared between experimental and control conditions. The results showed blocking of timing accuracy of a long (30-s) stimulus by a short (10-s) stimulus, but no evidence for overshadowing of timing accuracy.     

Plasma luteinizing hormone and testosterone concentrations in different breeds of young beef bulls in the tropics

Plasma concentrations of luteinizing hormone (LH) and testosterone were measured at 3, 8, and 11 months of age in 48 Africander cross (AX), 24 Brahman cross (BX), 21 Hereford-Shorthorn, selected (HSS) and 14 Hereford-Shorthorn, random-bred (HSR) bulls. In all breeds plasma LH was lower (P less than 0.01) at 8 months (1.7 ng/ml) than at 3 months (2.6 ng/ml) or at 11 months (2.6 ng/ml). Over all ages there were no differences among breeds in mean plasma LH (AX 2.4, BX 2.4, HSS 1.8, HSR 2.2 ng/ml) and no breed X age interactions. In contrast, plasma testosterone increased significantly (P less than 0.01) with age at a faster rate in the AX breed, resulting in a significant (P less than 0.05) breed X age interaction. Testosterone concentrations, though similar among breeds at 3 months of age (0.45 ng/ml), were much higher (P less than 0.01) by 11 months in AX (2.56 ng/ml) than in BX (1.30 ng/ml), HSS (0.78 ng/ml) or HSR (0.66 ng/ml) bulls. Although LH did not differ among the breeds studied, the more pronounced increase in testosterone with age in the Africander cross bulls is consistent with the higher level of fertility commonly observed in this breed when compared to Brahman cross and Hereford-Shorthorn breeds during natural mating in Queensland.     

Human perceptual learning: The effect of pre-exposure schedule depends on task demands

The effects of the pre-exposure schedule (concurrent, intermixed, and blocked) to two similar visual stimuli were assessed in three different tasks. Participants were more accurate identifying one of two pre-exposed stimuli as the target by means of same/different judgments after concurrent than intermixed or blocked pre-exposures. Regardless of pre-exposure schedule, participants were accurate in identifying the same target stimulus in a subsequent multiple choice task. However, the other pre-exposed stimulus was incorrectly chosen as the target in a greater proportion after blocked than intermixed or concurrent pre-exposure. Finally, participants who received the blocked schedule showed a greater ability to construct the target in a puzzle test than those who received a concurrent or intermixed schedule. These results suggest that the effect of pre-exposure schedule may depend on task-specific demands. But all these results might be explained by a selective attention mechanism like that proposed by Gibson (1969) to account for perceptual learning.     

Nicotine-evoked conditioned responding is dependent on concentration of sucrose unconditioned stimulus

Previous studies have shown that the interoceptive nicotine conditional stimulus (CS) functions similarly to exteroceptive CSs such as lights or environments. For instance, the appetitive conditioned response (CR) evoked when nicotine is repeatedly paired with sucrose presentations (the unconditioned stimulus; US) is sensitive to changes in training dose (CS salience) and the contiguity between the CS effects and sucrose. The current study was conducted to extend this research by examining the possible role of US intensity in CR acquisition and maintenance. Rats were trained using one of four sucrose concentrations: 0, 4, 16, or 32% (w/v). On nicotine sessions (0.4 mg base/kg), rats received 36 deliveries (4 s each) of their assigned concentration intermittently throughout the session; sucrose was withheld on saline sessions. In all groups, an appetitive goal-tracking CR was acquired at a similar rate. However, the asymptotic CR level varied with sucrose concentration. The magnitude of the CR was increased in rats trained with higher sucrose US concentrations. These findings are consistent with previous Pavlovian conditioning research, and extend the conditions under which the nicotine state functions as an interoceptive conditional stimulus.     

Stimulus comparison in perceptual learning: roles of sensory preconditioning and latent inhibition

Rats were given exposure to a compound flavour (AX) and to one element of that compound (X). Two drinking tubes were made available to the rat on each exposure trial. For group concurrent (CNC) one tube contained AX and the other X. For groups alternating (ALT) and blocked (BLK), however, both tubes contained the same flavour (AX or X). Group ALT received AX and X on alternate trials; group BLK received AX in the first block of trials and X on the second, or vice versa. After an aversion had been established to X the groups were tested with AX. It was found that group ALT showed less generalization from X to AX than did group BLK. This difference was not accompanied by a parallel difference in the level of conditioning to X. However, group CNC showed both stronger conditioning to X and greater generalization from X to AX than groups ALT and BLK. Implications for the role of stimulus comparison in the perceptual learning effect are discussed.     

Estimation of the Extent of Synteny Between Tetraodon nigroviridis and Homo sapiens Genomes

This paper presents a genomic comparison between 20 sequenced BACs (or fragments of BACs) from Tetraodon nigroviridis and the human genome. A total of 199 fish genes were identified by informatics resources, together with their putative human orthologues. Comparisons of the localizations in both species led to the identification of 32 syntenic regions and a minimum of 131 rearrangements in these regions that occurred during independent evolution of these species. This made it possible to estimate the rate of genomic rearrangements that occurred per million years (and per megabase). This rate is comparable to that obtained by comparison of the Fugu rubripes shotgun sequence data to human data but is significantly higher that those obtained by comparing the human genome to mammalian genomes. Overall, it suggests that genomic evolution by rearrangement is not uniform within the vertebrate group.Sequence data for the genomic BAC clones have been deposited with the DDBJ/EMBL/GenBank Data Libraries under accession numbers BX629360, BX629354, BX629355, BX629356, BX629357, BX629358, BX629359, and BX629360.     

Effects of auditory frequency-shifts on zero and below-zero SCR habituation

The purpose of the present experiment was to test a procedure for the measurement of effects of zero- and below-zero habituation (BZH) on responding to frequency shifts in auditory stimuli. The present procedure avoided some of the drawbacks of other procedures, that is, long duration, ambiguity in the definition of BZH, and inadequate control procedures. Two groups received 18 stimulus presentations each; group 1 received first a tone of 1000 Hz 12 times, then 1400 Hz (test stimulus 1) 3 times, and 1850 Hz (test stimulus 2) 3 times. Group 2 received the same stimuli, but 3, 12, and 3 times, respectively. The procedure had the advantages of short duration of the experiment, zero habituation and BZH were operationally defined (as 3 and 12 stimulus presentations, respectively), and there were adequate control conditions since a control group that did not receive stimulus change on the relevant trial was employed. The results showed no effects of stimulus shifts on responding to the test stimuli. Group 2 responded significantly less than group 1 across trials, though, and this may be explained by an inhibitory process elicited by changes in weak stimulation during the habituation process.     

Aspects of compound-conditioning to gustatory stimuli in the housefly Musca domestica L.

Houseflies (Musca domestica L.) were trained in a compound-conditioning paradigm where the conditioning stimuli were water and 1% sodium chloride solution. The unconditioned stimulus was 16% sucrose solution. A high degree of conditioning was produced. Control experiments for pseudoconditioning and sensitization revealed that the response of the flies to the procedure were due to an associative process. Experiments with double-water conditioned stimuli and with an interval between stimulus presentations indicate that the marked response to the first conditioned stimulus may be due to stimulus generalization in which the water, rather than the salt component of both stimuli served as the learning cue.     

Chronic pre-exposure to methamphetamine following 31 days of withdrawal impairs sexual performance but not sexual conditioning in male Japanese quail

In the current study, male quail were administered methamphetamine (3.0 or 5.6mg/kg IP) or saline once daily for 10 days and locomotor activity was assessed. Following a 31-day withdrawal period, sexual conditioning trials were conducted such that a conditioned stimulus (CS) was presented prior to a copulatory opportunity with a female quail. Male quail treated with methamphetamine (5.6mg/kg) showed a decrease in locomotor activity from Trial 1 to Trial 10 suggesting a potential tolerance effect. Following the 31-day withdrawal period, all male quail that received the CS paired with a copulatory opportunity showed enhanced approach to the CS, regardless of treatment history. Thus, chronic pre-exposure to methamphetamine did not alter sexual conditioning. In contrast, chronic pre-exposure to methamphetamine (3.0mg/kg) decreased the frequency of successful copulations suggesting that it impaired sexual performance. The findings suggest that methamphetamine may differentially affect the neural circuitry involved in motivational systems compared with those involved in consummatory aspects of sexual behavior. These effects may last long after drug cessation.     

Auditory pre-experience modulates classification of affect intensity: evidence for the evaluation of call salience by a non-human mammal,the bat <Emphasis Type="Italic">Megaderma lyra</Emphasis>

Introduction

Immediate responses towards emotional utterances in humans are determined by the acoustic structure and perceived relevance, i.e. salience, of the stimuli, and are controlled via a central feedback taking into account acoustic pre-experience. The present study explores whether the evaluation of stimulus salience in the acoustic communication of emotions is specifically human or has precursors in mammals. We created different pre-experiences by habituating bats (Megaderma lyra) to stimuli based on aggression, and response, calls from high or low intensity level agonistic interactions, respectively. Then we presented a test stimulus of opposite affect intensity of the same call type. We compared the modulation of response behaviour by affect intensity between the reciprocal experiments.

Results

For aggression call stimuli, the bats responded to the dishabituation stimuli independent of affect intensity, emphasising the attention-grabbing function of this call type. For response call stimuli, the bats responded to a high affect intensity test stimulus after experiencing stimuli of low affect intensity, but transferred habituation to a low affect intensity test stimulus after experiencing stimuli of high affect intensity. This transfer of habituation was not due to over-habituation as the bats responded to a frequency-shifted control stimulus. A direct comparison confirmed the asymmetric response behaviour in the reciprocal experiments.

Conclusions

Thus, the present study provides not only evidence for a discrimination of affect intensity, but also for an evaluation of stimulus salience, suggesting that basic assessment mechanisms involved in the perception of emotion are an ancestral trait in mammals.

     

Blocking of spatial control by landmarks in rats

We investigated spatial blocking among landmarks in an open-field foraging task in rats. In Phase 1, rats were presented with A+ trials during which landmark (LM) A signaled the location of hidden food. In Phase 2, rats were given AX+ trials in which LM X served as a redundant spatial cue to the location of food. Additionally, BY+ trials were given as a within-subjects overshadowing-control procedure. At test, rats received nonreinforced presentations of LM X and LM Y on separate trials. Rats took longer to find the training goal location in the presence of LM X than of LM Y, thereby demonstrating that spatial control by LM X was blocked by prior learning with LM A. This constitutes the first evidence in rats for spatial blocking of one proximal landmark by another—approximating a conventional blocking design.     

Opposite influence of perceptual memory on initial and prolonged perception of sensory ambiguity

Observers continually make unconscious inferences about the state of the world based on ambiguous sensory information. This process of perceptual decision-making may be optimized by learning from experience. We investigated the influence of previous perceptual experience on the interpretation of ambiguous visual information. Observers were pre-exposed to a perceptually stabilized sequence of an ambiguous structure-from-motion stimulus by means of intermittent presentation. At the subsequent re-appearance of the same ambiguous stimulus perception was initially biased toward the previously stabilized perceptual interpretation. However, prolonged viewing revealed a bias toward the alternative perceptual interpretation. The prevalence of the alternative percept during ongoing viewing was largely due to increased durations of this percept, as there was no reliable decrease in the durations of the pre-exposed percept. Moreover, the duration of the alternative percept was modulated by the specific characteristics of the pre-exposure, whereas the durations of the pre-exposed percept were not. The increase in duration of the alternative percept was larger when the pre-exposure had lasted longer and was larger after ambiguous pre-exposure than after unambiguous pre-exposure. Using a binocular rivalry stimulus we found analogous perceptual biases, while pre-exposure did not affect eye-bias. We conclude that previously perceived interpretations dominate at the onset of ambiguous sensory information, whereas alternative interpretations dominate prolonged viewing. Thus, at first instance ambiguous information seems to be judged using familiar percepts, while re-evaluation later on allows for alternative interpretations.     

Incubation of conditional suppression is an associatively-based phenomenon

Ten rats were deprived of water and trained to lick a tube for saccharin reinforcement. In each of the two sessions that followed, the rats received six contiguous pairings of a 30-second illumination of the houselight and a 0.75 second, 0.10 mA electric shock while licking. No sign of conditioning was observed during the first experimental session, but profound conditioning was observed on the first and subsequent trials of the second conditioning session. No comparable change in the rate of licking was observed in groups of rats that received only presentations of the visual stimulus, only presentations of the electric shock, or random presentation of the visual stimulus and electric shock during the first conditioning session. These data establish that the incubation of conditional suppression is an associative phenomenon.