Attenuation of latent inhibition after compound pre-exposure: Associative and perceptual explanations

Three experiments used rats as subjects and the conditioned emotional response (CER) paradigm to examine the effect of pre-exposure to a compound stimulus on the extent of latent inhibition to an element of that compound. In Experiment 1a a group of rats exposed to a compound that comprised a tone and a click exhibited less latent inhibition to the tone than did a group that had received pre-exposure to the tone in isolation. Experiment 1b showed that pre-exposure to the tone/click compound also resulted in an attenuation of latent inhibition to the click relative to a group that was pre-exposed to the click in isolation. Experiment 2 demonstrated that latent inhibition to the tone was left intact following pre-exposure to the tone in compound with a light. This pattern of results seems to be most plausibly explained in terms of the presence and absence of generalization decrement following compound pre-exposure.     

Latent learning and latent inhibition in maze discriminations

Rats were trained on an elevated maze where the rewarded alternative was defined either in terms of intra-maze or in terms of extra-maze cues. Pre-exposure to these cues produced a small latent or perceptual learning effect, i.e. facilitated subsequent learning of both problems, by comparison with animals pre-exposed to the maze with no cues present. Experiment 2 examined whether the effect of pre-exposure on intra-maze discrimination learning varied with the nature of the intra-maze cues. When positive and negative arms were further differentiated by painting the walls white and black, a marginal perceptual learning effect was turned into significant latent inhibition, i.e. a retardation of subsequent learning. Pre-exposure thus reliably facilitated extra-maze discrimnation learning, and its beneficial effects on intra-maze discrimination could be reversed by reducing the overlap between the intra-maze cues. Perceptual learning may therefore depend on requiring animals to discriminate between stimuli containing many common elements.     

Context-dependent latent inhibition in taste aversion learning

The effects of taste stimulus preexposure, either in the presence or in the absence of a specific contextual cue consisting of a specific noise-producing bottle, upon the conditioning and testing of conditioned taste aversions to the taste (saccharin) plus context (noisy-bottle) compound stimulus were investigated. Four groups of rats were given preexposure trials (latent inhibition) to either: (1) novel saccharin in novel noisy bottles, (2) novel saccharin in familiar silent bottles, (3) familiar water in novel noisy bottles, (4) familiar water in familiar silent bottles, in six trials. During conditioning, saccharin was presented in the noisy bottles followed by lithium chloride for all the groups. At testing, saccharin was presented in the noisy bottles for both one-bottle and two-bottle tests of aversion. It was indicated that the conditioning decrement produced after both saccharin and noisy bottle preexposure was overwhelmingly greater than any produced after preexposure to the elements. These results, discussed in relation to current theories of latent inhibition and perceptual learning, further underline the overwhelming significance of exteroceptive contextual elements in conditioned taste aversions.     

Effects of exposure to a to-be-shocked environment upon the rat's freezing response: Evidence for facilitation, latent inhibition, and perceptual learning

Three experiments used the freezing response of rats to examine the effects of pre-exposure to an environment upon (1) its associability with shock and (2) its discriminability from a second environment. Experiments 1 and 2 demonstrated that freezing was proportional to the interval between exposure to the environment at time T1 and the occurrence of shock at T2. This function was shifted by pre-exposure to the to-be-shocked environment, with brief pre-exposures increasing (facilitation) and extended pre-exposures decreasing (latent inhibition) the impact of a given T1-T2 interval on freezing. Experiment 3 provided evidence that the facilitatory and latent inhibitory effects resulting from brief and extended exposures to the to-be-shocked environment were accompanied by an increase in discriminability. The results were taken to have supported the claim that pre-exposure changes associability as well as discriminability (Hall & Honey, 1989) and were discussed in terms of the model for perceptual learning proposed by McLaren, Kaye, and Mackintosh (1990).     

Dissociation of rapid response learning and facilitation in perceptual and conceptual networks of person recognition

Repetition priming is a prominent example of non‐declarative memory, and it increases the accuracy and speed of responses to repeatedly processed stimuli. Major long‐hold memory theories posit that repetition priming results from facilitation within perceptual and conceptual networks for stimulus recognition and categorization. Stimuli can also be bound to particular responses, and it has recently been suggested that this rapid response learning, not network facilitation, provides a sound theory of priming of object recognition. Here, we addressed the relevance of network facilitation and rapid response learning for priming of person recognition with a view to advance general theories of priming. In four experiments, participants performed conceptual decisions like occupation or nationality judgments for famous faces. The magnitude of rapid response learning varied across experiments, and rapid response learning co‐occurred and interacted with facilitation in perceptual and conceptual networks. These findings indicate that rapid response learning and facilitation in perceptual and conceptual networks are complementary rather than competing theories of priming. Thus, future memory theories need to incorporate both rapid response learning and network facilitation as individual facets of priming.     

Context specificity of latent inhibition in taste aversion learning

In three experiments rats were given injections of LiCl after consuming distinctively flavoured water. The rats developed an aversion to the flavour and in all experiments the magnitude of the aversion was found to be reduced in subjects that had received pre-exposure to the flavour without aversive consequences. Experiment 1 demonstrated this pre-exposure effect to be a case of latent inhibition. The remaining experiments investigated the effects of pre-exposing the flavour in a context different from that used for conditioning. It was found (Experiment 2) diat latent inhibition transferred perfectly when the context change consisted of a move from one home cage to another. Context specificity of latent inhibition was found (Experiment 3) only when the subjects were given daily sessions in die experimental contexts, these being cages different from the home cage.     

Some determinants of latent inhibition in human predictive learning

The present experiments assessed the effects of different manipulations between cue preexposure and cue-outcome pairings on latent inhibition (LI) in a predictive learning task with human participants. To facilitate LI, preexposure and acquisition with the target cues took place while participants performed a secondary task. Presentation of neither the target cues nor the target outcome was anticipated based on the instructions. Experiment 1 demonstrated the LI effect in the new experimental preparation. Experiment 2 analyzed the impact on LI of different activities that participants performed during the interval between preexposure and acquisition. Experiment 3 assessed LI as a function of changes in the secondary task cues made between preexposure and acquisition, namely presenting novel cues and reversing the cue-outcome contingencies. All of the manipulations in Experiments 2 and 3 resulted in a decrease in LI. The attenuation of LI by these manipulations challenges most current theories of learning and is best accommodated by Conditioned Attention Theory (Lubow, Weiner, & Schnur, 1981).     

Feedback and stimulus-offset timing effects in perceptual category learning

We examined how feedback delay and stimulus offset timing affected declarative, rule-based and procedural, information–integration category-learning. We predicted that small feedback delays of several hundred milliseconds would lead to the best information–integration learning based on a highly regarded neurobiological model of learning in the striatum. In Experiment 1 information–integration learning was best with feedback delays of 500 ms compared to delays of 0 and 1000 ms. This effect was only obtained if the stimulus offset following the response. Rule-based learning was unaffected by the length of feedback delay, but was better when the stimulus was present throughout feedback than when it offset following the response. In Experiment 2 we found that a large variance (SD = 150 ms) in feedback delay times around a mean delay of 500 ms attenuated information–integration learning, but a small variance (SD = 75 ms) did not. In Experiment 3 we found that the delay between stimulus offset and feedback is more critical to information–integration learning than the delay between the response and feedback. These results demonstrate the importance of feedback timing in category-learning situations where a declarative, verbalizable rule cannot easily be used as a heuristic to classify members into their correct category.     

On the relationship between autobiographical memory and perceptual learning

Although the majority of research on human memory has concentrated on a person's ability to recall or recognize items as having been presented in a particular situation, the effects of memory are also revealed in a person's performance of a perceptual task. Prior experience with material can make that material more easily identified or comprehended in perceptually difficult situations. Unlike with standard retention tests, effects of prior experience on a perceptual task do not logically require that a person be aware that he or she is remembering. Indeed, amnesic patients purportedly show effects of practice in their subsequent performance of a perceptual or motor task even though they profess that they do not remember having engaged in that prior experience. The experiments that are reported were designed to explore the relationship between the more aware autobiographical form of memory that is measured by a recognition memory test and the less aware form of memory that is expressed in perceptual learning. Comparisons of effects on perceptual learning and recognition memory reveal two classes of variables. Variables such as the level of processing of words during study influenced recognition memory, although they had no effect on subsequent perceptual recognition. A study presentation of a word had as large an effect on its later perceptual recognition when recognition memory performance was very poor as it did when recognition memory performance was near perfect. In contrast, variables such as the number and the spacing of repetitions produced parallel effects on perceptual recognition and recognition memory. Following Mandler and others, it is suggested that there are two bases for recognition memory. If an item is readily perceived so that it seems to "jump out" from the page, a person is likely to judge that he or she has previously seen the item in the experimental situation. Variables that influence ease of perceptual recognition, then, can also have an effect on recognition memory, so parallel effects are found. The second basis for recognition memory involves elaboration of a word's study context and depends on such factors as level of processing during study--factors that are not important for perceptual recognition of isolated words. Comparisons of perceptual recognition and recognition memory are shown to be useful for determining how a variable has its effect. Effects of study on perceptual recognition appear to be totally due to memory for physical or graphemic information. Results reported are also relevant to theories of perceptual learning. A single presentation of an item is shown to have large and long-lasting effects on its later perceptual recognition. At least partially, effects of study on perceptual recognition depend on the same variables as do effects on more standard memory tests.     

Conditioned and latent inhibition in taste-aversion learning: clarifying the role of learned safety.

Experiments 1-3 investigated the applicability of the classical conditioning concept of conditioned inhibition to taste-aversion learning. Rats made ill after drinking saccharin and subsequently administered a "safe" exposure to saline (or casein hydrolysate) evidenced an enhanced preference for the safe fluid (relative to either a third, slightly aversive, solution or to water) when compared to controls in which saccharin was not previously poisoned. Such active condition inhibition was significantly reduced in Experiment 4 when two safe exposures to saline preceded saccharin-illness pairings. These results indicate that conditioned inhibition can be established in a taste-aversion procedure and that a latent inhibition manipulation reduces the ability of a taste to become a signal for safety. Implications of these findings for the learned safety theory of taste-aversion learning and the relevance to bait-shyness of principles established within the classical conditioning paradigm are considered.     

When more is less: feedback effects in perceptual category learning

Rule-based and information-integration category learning were compared under minimal and full feedback conditions. Rule-based category structures are those for which the optimal rule is verbalizable. Information-integration category structures are those for which the optimal rule is not verbalizable. With minimal feedback subjects are told whether their response was correct or incorrect, but are not informed of the correct category assignment. With full feedback subjects are informed of the correctness of their response and are also informed of the correct category assignment. An examination of the distinct neural circuits that subserve rule-based and information-integration category learning leads to the counterintuitive prediction that full feedback should facilitate rule-based learning but should also hinder information-integration learning. This prediction was supported in the experiment reported below. The implications of these results for theories of learning are discussed.     

Extinction and latent inhibition of within-event learning are context specific

Exposure to a solution composed of an odor (almond) and a taste (salt) produced a context-independent preference when rats were subsequently tested with almond under a salt appetite. Postcompound exposure to either the almond or the salt alone reduced almond preferences but only when rats were tested in the extinction context. Exposure to either the almond or the salt in 1 context in advance of exposure to the compound in a different context also reduced preferences but only when the rats were tested in the context in which the element had been pre-exposed. These results show that extinction and latent inhibition of within-event learning are context specific.     

On the relation between auditory spatial attention and auditory perceptual asymmetries

Laterality investigators have typically interpreted any perceptual asymmetry as a direct expression of the functional organization of the brain. However, many other confounding factors, including the asymmetric distribution of attention, may also contribute to either the magnitude or the direction of any of these advantages. In two experiments, attention was manipulated in a dichotic listening paradigm by presenting a preexposural tone cue to the ear from which the subject was required to report. The time available to orient attention was manipulated by varying the time period between the onset of the cue and the onset of the trial (stimulus onset asynchrony, or SOA).Results indicated that a right ear advantage for the identification of verbal material obtained at a 150-msec SOA was almost completely eliminated at an SOA of 450 msec. In addition, the direction of the ear advantage for emotion identification was found to depend on task difficulty. A left ear advantage, apparent when task difficulty was minimal, was reversed to a right ear advantage when difficulty was increased. These data are taken as evidence that, when subjects are faced with a difficult dichotic task, there is a general tendency for right-handed subjects to bias their attention toward the right ear. Such a tendency is shown not only to have likely seriously compromised the results of past investigations of functional perceptual asymmetries but also to be inconsistent with previously proposed theories of dichotic listening performance.     

Transfer of spatial behavior between different environments: implications for theories of spatial learning and for the role of the hippocampus in spatial learning

In 3 experiments, rats were required to find a submerged platform located in 1 corner of an arena that had 2 long and 2 short sides; they were then trained to find the platform in a new arena that also had 2 long and 2 short sides but a different overall shape. The platform in the new arena was easier to find if it was in a corner that was geometrically equivalent, rather than the mirror image, of the corner where it had previously been located. The final experiment revealed that hippocampal lesions impaired rats' ability to find the platform in these arenas. The results suggest that rats did not use the overall shape of the arena to locate the platform but relied on more local cues and that the hippocampus plays a role in navigation based on these cues.     

Combining letter-matching and tone discrimination: Evidence of automatic perceptual and spatial congruity effects

Dual task and priming paradigms were combined to investigate the distinction between automatic and attentional processes. Subjects in two experiments performed a primed letter-matching and a tone discrimination task separately and concurrently. The interval between prime onset and letter pair (SOA) was varied from 50 to 500 msec. Cost-benefit analyses in Experiment 1 indicated that primes that matched target letter pairs began to facilitate performance at an SOA of 150 msec. Primes inhibited performance when they mismatched identical letter pairs at SOA 100. In the dual-task situation, the benefits of priming letter targets were reflected in probe latencies with no evidence of concurrent costs in tone latencies. Experiment 2 revealed that two tasks could be primed simultaneously as effectively as when each was primed alone. Findings are discussed in reference to Posner and Snyder's (1975a, 1975b) two-process theory of priming and the applicability of a secondary task technique.     

On the relation between auditory spatial attention and auditory perceptual asymmetries.

Laterality investigators have typically interpreted any perceptual asymmetry as a direct expression of the functional organization of the brain. However, many other confounding factors, including the asymmetric distribution of attention, may also contribute to either the magnitude or the direction of any of these advantages. In two experiments, attention was manipulated in a dichotic listening paradigm by presenting a preexposural tone cue to the ear from which the subject was required to report. The time available to orient attention was manipulated by varying the time period between the onset of the cue and the onset of the trial (stimulus onset asynchrony, or SOA). Results indicated that a right ear advantage for the identification of verbal material obtained at a 150-msec SOA was almost completely eliminated at an SOA of 450 msec. In addition, the direction of the ear advantage for emotion identification was found to depend on task difficulty. A left ear advantage, apparent when task difficulty was minimal, was reversed to a right ear advantage when difficulty was increased. These data are taken as evidence that, when subjects are faced with a difficult dichotic task, there is a general tendency for right-handed subjects to bias their attention toward the right ear. Such a tendency is shown not only to have likely seriously compromised the results of past investigations of functional perceptual asymmetries but also to be inconsistent with previously proposed theories of dichotic listening performance.