The temporal dynamics of a visual discrimination: The role of stimulus comparison and opponent processes.

The influence of trial spacing on simple conditioning is well established: When successive reinforced conditioned stimulus, CS+, trials are separated by a short interval (massed training), conditioned responding emerges less rapidly than when such trials are separated by longer intervals (spaced training). This study examined the influence of trial spacing on the acquisition of an appetitive visual discrimination in rats. Experiments 1 and 2 established that massed training facilitates the acquisition of such discriminations. The results of subsequent experiments demonstrated that this trial-spacing effect reflects the proximity of nonreinforced, CS-, trials to preceding (Experiment 3) and signaled (Experiment 4) presentations of the reinforcer. Experiment 5 showed that the facilitation of discrimination learning with massed training reflected an effect on learning rather than performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intertrial interval effects in classically conditioned fear to a discrete conditioned stimulus and to situational cues.

In Exp I fear was classically conditioned in a total of 240 female hooded and Sprague-Dawley rats with a discrete conditioned stimulus (CS) at intertrial intervals (ITIs) of 15, 45, 75, 105, 165, or 225 sec and in Exp II, with an additional 144 Ss, with or without a discrete CS at ITIs of 165, 225, or 285 sec. The amount of fear conditioned to situational cues and to the discrete CS plus situational cues was then measured by the learning of a hurdle-jumping response which allowed escape from the fear-eliciting stimuli. Results suggest that as ITI was lengthened fear conditioned to situational cues alone and to the discrete CS increased. However, following conditioning with a discrete CS, fear elicited by situational cues increased with ITI but then decreased, presumably because a discrimination had been formed between the situational cues and the compound of CS plus situational cues. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential effects of training intertrial interval on acquisition of trace and long-delay fear conditioning in rats.

Many factors govern conditioning effectiveness, including the intertrial interval (ITI) used during training. The present study systematically varied the training ITI during both trace and long-delay fear conditioning. Rats were trained using one of six different ITIs and subsequently tested for conditioning to the white noise conditioned stimulus (CS) and the training context. After trace conditioning, percent freezing to the CS was positively correlated with training ITI, whereas percent freezing to the context was negatively correlated with training ITI. In contrast, when rats were trained using a long-delay paradigm, freezing during the CS test session did not vary as a function of training ITI; rats exhibited robust freezing at all ITIs. The long-delay conditioned rats exhibited relatively low levels of freezing during the context test. Thus, trace is more sensitive than long-delay fear conditioning to variations in the training ITI. These data suggest that training ITI is an important variable to consider when evaluating age or treatment effects, where the optimal ITI may vary with advancing age or pharmacological treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The trial spacing effect in delayed matching-to-sample by pigeons is dependent upon the illumination condition during the intertrial interval.

Two experiments examined the effects of chamber illumination during the intertrial interval (ITI) of delayed matching-to-sample by 8 White Carneaux pigeons. Exp I demonstrated that accurate choice of the matching stimulus was disrupted by illumination at long ITIs but not short ITIs. This effect was obtained regardless of the ITI illumination condition during training. The disruption produced by long illuminated ITIs was constant across delay intervals. A strong direct linear relationship between matching accuracy and the log ITI/delay ratio was obtained when the ITI was dark but not when it was illuminated. In Exp II, ITI illumination was more disruptive when it occurred at the end rather than at the beginning of the ITI. Results support the view that trial spacing effects are not due to competing memories from previous trials. A change in ITI illumination may disrupt encoding of the sample stimulus and offset the beneficial effects of trial spacing. (French abstract) (23 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Antagonism of NMDA receptors impairs acquisition but not retention of olfactory memory.

Examined the effect of chronic intraventricular administration of D-amino-phosphono-valeric acid (AP5), a competitive NMDA receptor antagonist, on olfactory discrimination and avoidance learning. 20 rats previously trained to solve a series of discriminations between 2 simultaneously presented odors were infused with either 20 mM D-AP5 or saline for 14 days. An important and unusual feature of the paradigm was that it permitted a comparison of drug effects on acquisition of new discriminations vs retention of old ones. Animals treated with AP5 made significantly more errors than did controls in acquiring discriminations between low-intensity odors presented with long intertrial intervals (ITIs). However, no deficit was observed when short ITIs or strong odors were used. Animals treated with AP5 had no difficulty in recognizing odors on which they were trained before administration of the drug. After exhaustion of the pumps, performance of the AP5 group was indistinguishable from that of the control group. One-way active avoidance learning was not affected by chronic infusion of AP5. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Duration of signals for intertrial reinforcement and nonreinforcement in random control procedures.

In the random control procedure, responding to a conditioned stimulus (target CS) is prevented when the probability of unsignaled, unconditioned stimuli (UCS) in the intertrial interval (ITI) is equal to the probability of the UCS in the presence of the target CS. Three experiments used an autoshaping procedure with White Carneaux pigeons to examine the effects of the temporal duration of signals for the ITI UCS (cover CSs) and for concomitant periods of nonreinforcement. In Experiment 1, a short duration cover, but not a long duration cover, resulted in responding to the target CS. In Experiment 2, an explicit CS– cue during periods of nonreinforcement did not affect target acquisition. In Experiment 3, a long CS–, but not a short cover CS, was a sufficient condition for the acquisition of responding to the target CS. These results imply that the acquisition of responding to a target CS requires a discriminable period of nonreinforcement that is long relative to the target CS duration. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Strain distribution of mice in discriminated Y-maze avoidance learning: Genetic and procedural differences.

The current study was conducted to characterize discriminated avoidance learning in mice by using a Y-maze task. In Experiment 1, the task parameters were manipulated, including the amount of time spent in the start arm, the amount of time to make the avoidance response, and the intertrial interval (ITI) using C57?×?SJL F1 hybrid mice. Avoidance performance was significantly improved with longer times to avoid the shock and longer ITIs. In Experiment 2, mice from 4 inbred strains (BALB/cByJ, DBA/2J, C57BL/6J, and SJL/J), an F1 hybrid (C57?×?SJL), and 1 outbred strain (CD1) were tested with various ITIs. Strain differences were observed in avoidance learning, with BALB, DBA, C57?×?SJL and CD1 mice showing significantly better avoidance learning than C57 mice, which were better than SJL mice. These data demonstrate that Y-maze performance is significantly influenced by the genetic background of the mouse and the parameters of the task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Backward inhibitory conditioning with signaled and unsignaled unconditioned stimuli: Distribution of trials across days and intertrial interval.

Through summation tests in conditioned suppression with rats we assessed the effects of distribution of trials across days (Experiment 1) and intertrial interval (ITI) (Experiment 2) on the degree of backward conditioned inhibition established through signaled and unsignaled unconditioned stimuli (USs). Two backward conditioned inhibitory stimuli (CS-s) were established within subjects: One backward CS- followed signaled shocks; the other followed unsignaled shocks. After 12 daily sessions (Experiment 1), the signaled backward CS- was strongly inhibitory and significantly more inhibitory than the unsignaled backward CS-. When the same number of trials occurred in a single long session, performances to both CS-s converged at moderate levels. At the 90-s ITI, (Experiment 2) the signaled and unsignaled backward CS-s were nearly equivalent in effectiveness. When the ITI was 540 s, performances diverged, and signaled backward CS- was substantially more effective; the longer ITI facilitated inhibitory backward conditioning based upon signaled USs but prevented the development of inhibitory backward conditioning based upon unsignaled USs. These functionally opposite effects on backward conditioned inhibition, depending on whether the US was signaled or not, are anticipated by Wagner's "standard operating procedure" (SOP) model of short-term memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hemostatic and fibrinolytic indices in neonatal foals with presumed septicemia

Gerbils learned to approach a spatial-olfactory stimulus that signaled access to their pairmate. Experiments 1 and 3 used a discrimination procedure in which 1 conditioned stimulus (the CS+) was presented immediately before access to the pairmate and another (the CS-) was presented alone. Both male and female gerbils came to approach the CS+ sooner than the CS- and spent more time near the CS+ than the CS-. Discrimination learning was facilitated by making the CS+ and CS- spatially distinct (Experiment 3). Learning also was demonstrated in male gerbils, using a between-subjects design with a single CS. Pairing the CS with the opportunity for social interaction resulted in greater approach to the CS within 10 trials than presenting the CS and social opportunity in an unpaired fashion (Experiment 2). These findings demonstrate social-affiliative learning in the Mongolian gerbil. Similarities and differences between these findings and sexual conditioning effects in other species are discussed.     

Pavlovian conditioning of social affirmative behavior in the Mongolian gerbil (Meriones unguiculatus).

Gerbils learned to approach a spatial-olfactory stimulus that signaled access to their pairmate. Experiments 1 and 3 used a discrimination procedure in which 1 conditioned stimulus (the CS+) was presented immediately before access to the pairmate and another (the CS–) was presented alone. Both male and female gerbils came to approach the CS+ sooner than the CS– and spent more time near the CS + than the CS–. Discrimination learning was facilitated by making the CS+ and CS– spatially distinct (Experiment 3). Learning also was demonstrated in male gerbils, using a between-subjects design with a single CS. Pairing the CS with the opportunity for social interaction resulted in greater approach to the CS within 10 trials than presenting the CS and social opportunity in an unpaired fashion (Experiment 2). These findings demonstrate social-affiliative learning in the Mongolian gerbil. Similarities and differences between these findings and sexual conditioning effects in other species are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of signaling intertrial unconditioned stimuli in autoshaping.

Context–UCS associations have been suggested as the mediator of the response decrement that occurs when extra UCSs are added to the intertrial intervals (ITIs) of a standard Pavlovian conditioning situation. The present autoshaping experiments were concerned with the effect of signaling those extra UCSs, since such signaling might be expected to lessen their ability to condition the context. In Exp I, 16 female Carneaux pigeons were trained in Skinner boxes before receiving pretraining with the CS to be used as the signal of the ITI UCSs. During the main training, Ss were given autoshaping with a keylight CS. Exp II used a tone CS with 31 Ss. Results show that signaling the ITI UCSs did reduce their detrimental effects in responding to the CS. To determine whether that reduction was due to an impact of signaling on the target-CS/UCS association or on performance to the target-CS, Exp III examined responding to differentially trained CSs in a common context, as well as responding to identically trained CSs in differentially trained contexts with 32 Ss. More responding occurred to the CS trained with signaled, as compared with unsignaled, ITI UCSs; further, there was more responding to that CS in the more highly valued context. Results suggest that contextual value does interact with CS–UCS learning and may also affect performance to the CS. (42 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Two kinds of attention in Pavlovian conditioning: Evidence for a hybrid model of learning.

Four appetitive Pavlovian conditioning experiments with rats examined the rate at which the discrimination between compounds AY and AX was solved relative to the discrimination between compounds AY and BY. In Experiments 1 and 2, these discriminations were preceded by training in which A and B were continuously reinforced and X and Y were partially reinforced. Consistent with the Pearce and Hall (1980) model, the results showed that the AY/AX discrimination was solved more readily than the AY/BY discrimination. In Experiments 3 and 4, the discriminations were preceded by feature-positive training in which trials with AX and BY signaled food but trials with X and Y did not. Consistent with the Mackintosh (1975) model, the results showed that the AY/BY discrimination was solved more readily than the AY/AX discrimination. These results are discussed with respect to a hybrid model of conditioning and attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The ontogeny of interstimulus interval (ISI) discrimination of the conditioned eyeblink response in rats.

Discrimination of the eyeblink conditioned response (CR) between conditioned stimuli (CSs) of different durations and modalities was examined across development in rats. Interstimulus interval (ISI) discrimination was evident at Postnatal Days 23-34 in Experiment 1, and earlier CR peak latencies and enhanced CR amplitudes were seen to the long CS in the ISI discrimination group relative to a control group receiving the short CS without reinforcement. Experiment 2 showed that early CR peak latencies and enhanced CR amplitudes to the long CS in the ISI discrimination group were due to associative pairing of the short CS and unconditioned stimulus. Experiment 3 demonstrated ISI discrimination in adults that was improved relative to younger subjects, but with no enhancement of CR amplitude to the long CS in the ISI discrimination group. Cerebellar cortical maturation may influence the ontogeny of CR timing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Classical nictitating membrane conditioning in the rabbit (Oryctolagus cuniculus): Single alternation with differential intertrial intervals.

Investigated single alternation (SA) patterning behavior in 24 albino New Zealand rabbits by varying in 7 experiments the intertrial intervals (ITIs) following reinforced (R) and nonreinforced (N) trials. When short ITIs followed R trials and long ITIs followed N trials, reliable SA patterning was obtained. Neither (a) the presence of differential ITI cues, (b) the short ITIs prior to the N trials, nor (c) the early position of the N trial within the R-R interval were sufficient in and of themselves to support substantial patterning behavior; instead, each of these features apparently contributed to the patterning effect in a combined fashion. It is concluded that R- and N-trial aftereffects do not play an important role in conditioning the rabbit nictitating membrane. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Patterned (single) alternation in infant rats after combined or separate lesions of hippocampus and amygdala.

The role of the developing hippocampus and the amygdala on patterned (single) alternation (PA) in the infant rat was investigated in 4 experiments. In Exps 1 and 2, Ss were given 2 bilateral electrolytic hippocampal lesions or sham surgeries at 10 or 11 days of age and were trained 6 days later in a straight runway. In Exp 1, there were 120 trials in 1 day, with an 8-, a 15-, or a 30-s intertrial interval (ITI). PA learning occurred in lesion and sham Ss at the 8- and 15-s ITIs. In Exp 2, training was extended to 240 trials over 2 days, with a 30- or 60-s ITI. Sham and lesion Ss showed PA at the 30-s ITI, but the emergence of PA was delayed in the lesion pups at the 60-s ITI. In Exp 3, amygdaloid lesions had no effect on PA learning at the 8-s ITI. However, when Ss with hippocampal and amygdaloid lesions were trained at the 8-s ITI, the emergence of PA was delayed, and its size was reduced (Exp 4). Results argue for a role of the hippocampus in PA learning at long ITIs and suggest that, even in 16-day-old Ss exposed to an 8-s ITI, the combined hippocampal and amygdaloid lesion produces a deficit greater than either the hippocampal or the amygdaloid lesion. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of signals for unconditioned stimulus absence in the sensitivity of autoshaping to contingency.

Pigeons autoshape to a keylight conditioned stimulus (CS) that is poorly correlated with a food unconditioned stimulus (UCS) if UCSs occurring in the absence of the CS are signaled by some other cue. Three experiments examined if this is because signaling blocks context conditioning or because it converts the intertrial interval (ITI) into a predictor of UCS absence. Results indicated that cuing periods of UCS absence was not sufficient for acquisition. Signaling failed to produce acquisition if the signal also accompanied the CS, although this procedure converts the ITI into a predictor of UCS absence. The detrimental effect of compounding the signal with the CS occurred only if the signal was separately paired with the UCS, which suggests it was due to blocking of the CS by the signal. The results suggested that the signaling effect depends on blocking of the context by the signal, not on conversion of the ITI into a signal for UCS absence. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interactive contributions of intracellular calcium and protein phosphatases to massed-trials learning deficits in Hermissenda.

Using Hermissenda as subjects, massed-trials training deficits were examined. Associative pairings of light and rotation induced a progressively greater conditioned foot contraction in response to light as the intertrial interval (ITI) was extended (up to 8 min). In contrast, a short ITI (30 s) produced no evidence of learning. In a corresponding in vitro conditioning experiment that mimicked training of the intact animal, facilitation of neuronal excitability in the animal's B photoreceptors paralleled the results obtained in vivo. Imaging of intracellular Ca2+ using Fura-2 indicated that Ca2+ levels remained elevated during short ITIs. This Ca2+ accumulation appears to induce activation of protein phosphatases because normal facilitation of the B photoreceptors was induced with a short ITI if training occurred in the presence of a phosphatase inhibitor. These results suggest that intracellular Ca2+ and protein phosphatases contribute interactively to the kinetics of memory formation and provide evidence that an accumulation of intracellular Ca2+ across training trials may impede memory formation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acquisition of categorical color perception: A perceptual learning approach to the linguistic relativity hypothesis.

Color perception can be categorical: Between-category discriminations are more accurate than equivalent within-category discrimination. The effects could be inherited, learned, or both. The authors provide evidence that supports the possibility of learned categorical perception (CP). Experiment 1 demonstrated that observers' color discrimination is flexible and improves through repeated practice. Experiment 2 demonstrated that category learning simulates effects of "natural" color categories on color discrimination. Experiment 3 investigated the time course of acquired CP. Experiment 4 found that CP effects are acquired through hue- and lightness-based category learning and obtained interesting data on the dimensional perception of color. The data are consistent with the possibility that language may shape color perception and suggest a plausible mechanism for the linguistic relativity hypothesis. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learning and memory of odor-reward association: Selective impairment following horizontal diagonal band lesions.

Rats with horizontal diagonal band of Broca (HDBB) lesions were trained in a successive-cue olfactory discrimination using different intertrial intervals (ITIs). They learned the paradigm of the task, but substantial impairment in performance of odor–reward associations was observed when the ITIs were longer than 15 sec. They performed as well as control animals with short ITIs when they were trained previously with long ITIs, but forgetting appeared very soon thereafter (24 hrs later). The finding is that the HDBB is an essential relay between the hippocampal system and the olfactory cortex. The HDBB allows associative memory storage when a limited-duration short-memory system located elsewhere is overlooked. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Relationships between the determinants of performance in serial feature-positive discriminations.

Conducted 3 experiments using an appetitive behavioral observation procedure to investigate the effects of pre- and postdiscrimination treatments on learning and performance in serial feature-positive discriminations. Previous work suggests that performance in this discrimination is based on feature–UCS associations, feature–common element associations, and a conditional occasion-setting relation. Exp I examined the effects of prediscrimination reinforcement of the components of the discrimination. 26 male and 6 female Sprague-Dawley rats were assigned, in groups of 8, to 1 of 4 prereinforcement conditions (involving administration of a tone, a light, and a trace interval). Ss then trained on a serial feature-positive discrimination. Behavioral observations were recorded. Exps II and III investigated the effects of postdiscrimination nonreinforcement and reinforcement procedures on performance of established discriminative responding by 64 Ss. Results of the studies and of previous work are interpreted to show that the conditional occasion-setting relation may be independent of feature–UCS associations and may not depend on feature/common element associations. (61 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)