Response stereotypy without automaticity: Not quite involuntary attention in the pigeon

Previous research has shown that when pigeons are required to peck each of two keys four times in any order for reinforcement, stereotyped response sequences develop, though they are not required by the task. However, despite this stereotypy, sequences are not automatized. They require sufficient attention that sequence performance is disrupted by a concurrent, delayed matching-to-sample task. In the present experiments, pigeons were required to execute response sequences and delayed matching-to-sample concurrently. Experiment 1 showed that the matching task disrupts sequence performance even when the matching sample stimuli do not have to be processed concurrently with sequence execution. The presence of sample stimuli during sequence execution seems to command attention even if the sample stimuli are also available for processing when sequences are not being executed. Experiment 2 used the directed forgetting technique to show that pigeons do seem able to ignore sample stimuli if they are given information that tells them they will not be required to remember those stimuli later. Together, the experiments suggest attentional mechanisms in the pigeon that are not quite involuntary.     

Statistical Learning of Unfamiliar Sounds as Trajectories Through a Perceptual Similarity Space

In typical statistical learning studies, researchers define sequences in terms of the probability of the next item in the sequence given the current item (or items), and they show that high probability sequences are treated as more familiar than low probability sequences. Existing accounts of these phenomena all assume that participants represent statistical regularities more or less as they are defined by the experimenters—as sequential probabilities of symbols in a string. Here we offer an alternative, or possibly supplementary, hypothesis. Specifically, rather than identifying or labeling individual stimuli discretely in order to predict the next item in a sequence, we need only assume that the participant is able to represent the stimuli as evincing particular similarity relations to one another, with sequences represented as trajectories through this similarity space. We present experiments in which this hypothesis makes sharply different predictions from hypotheses based on the assumption that sequences are learned over discrete, labeled stimuli. We also present a series of simulation models that encode stimuli as positions in a continuous two‐dimensional space, and predict the next location from the current location. Although no model captures all of the data presented here, the results of three critical experiments are more consistent with the view that participants represent trajectories through similarity space rather than sequences of discrete labels under particular conditions.     

The representation of explicit motor sequence knowledge

Much research has investigated the representation of implicitly learned motor sequences: Do subjects learn sequences of stimuli, responses, response locations, or some combination? Most of the work on this subject indicates that when sequences are learned implicitly, it is in terms of response locations. The present work investigated the representation of explicitly learned motor sequences. In four experiments, we found consistent evidence that explicitly learned sequences are represented in terms of stimulus locations. This conclusion held true for both self-report measures (subjects said that they learned stimuli) and performance measures, but when stimuli changed, performance degraded. We interpret these data in a multiple-memory-systems framework.     

Novelty,complexity, and hedonic value

Two experiments, in which Ss were exposed to sequences of colored shapes, investigated effects on ratings of “pleasingness” and “interestingness” of variables that had previously been shown to affect ratings of “novelty.” The results indicate, on the whole, that both pleasingness and interestingness increase with novelty. These findings run counter to those of experiments indicating an inverse relation between novelty and verbally expressed preference. Two further experiments examined effects of some variables that might account for this apparent discrepancy. Homogeneous sequences declined in judged “pleasantness” more than sequences in which several stimuli were interspersed, and simple stimuli became less pleasant as they became less novel, while complex stimuli declined less or became more pleasant. The findings are related to hypotheses regarding mechanisms of hedonic value. Two crucial predictions were confirmed in a fifth experiment.     

The influence of grammatical, local, and organizational redundancy on implicit learning: an analysis using information theory

People behave as if they know the structure of their environment. Because people rarely study that structure explicitly, several theorists have postulated an implicit learning system that abstracts that structure automatically. An alternative view is that people respond to local structure that derives from global structure. Measures are developed that quantify structure in a set of stimuli, in individual stimuli, and in encoded stimuli. The authors apply the measures to examine serial recall for sequences of colors generated using a stationary Markov grammar. They demonstrate that the 3 kinds of redundancy are confounded and show that the memorial advantage for grammatical stimuli reflects participants' use of local expressions of grammatical structure to aid learning.     

Observational learning of two visual discriminations by pigeons: a within-subjects design.

Pigeon's observational learning of successive visual discrimination was studied using within-subject comparisons of data from three experimental conditions. Two pairs of discriminative stimuli were used; each bird was exposed to two of the three experimental conditions, with different pairs of stimuli used in a given bird's two conditions. In one condition, observers were exposed to visual discriminative stimuli only. In a second condition, subjects were exposed to a randomly alternating sequence of two stimuli where the one that would subsequently be used as S+ was paired with the operation of the grain magazine. In a third experimental condition, subjects were exposed to the performance of a conspecific in the operant discrimination procedure. After exposures to conspecific performances, there was facilitation of discriminative learning, relative to that which followed exposures to stimulus and reinforcement sequences or exposures to stimulus sequences alone. Exposure to stimulus and food-delivery sequences enhanced performance relative to exposure to stimulus sequences alone. The differential effects of these three types of exposure were not attributable to order effects or to task difficulty; rather, they clearly were due to the type of exposure.     

Extending sequence-class membership with matching to sample

Three normal adults were first trained to point sequentially to each member of several pairs of visual stimuli. This baseline training established one class of stimuli to which subjects responded first, and another class of stimuli to which they responded second. Then, in a matching-to-sample procedure, baseline-sequence stimuli served as samples and new visual stimuli served as comparisons. Subjects were trained to choose one group of new comparisons when the sample was a "first" stimulus from the sequence baseline, and to choose the other new comparison stimuli when the sample was a "second" from the sequence baseline. When the new stimuli were then presented as pairs in the posttest, two subjects pointed to them in sequences predictable on the basis of the stimulus-class membership established during matching to sample. The failure of one subject to demonstrate sequential transfer was shown to be a consequence of the failure of the matching-to-sample procedure to establish stimulus classes. The production of sequences that were not directly trained suggested an empirical approach to the analysis of simple grammatical behavior.     

Food-reinforced inhibition of conditioned salivation in dogs.

Twelve dogs salivated to a tone that was followed by food, but not to a noise for which there was an added response dependency. The noise was followed by food if and only if they did not salivate. The addition of this response dependency vitiated the classically conditioned response to the noise. A yoked-control group of 6 dogs receiving the same sequences of stimuli and food salivated to both the tone and noise stimuli.     

How modality specific is the iambic-trochaic law? Evidence from vision

The iambic-trochaic law has been proposed to account for the grouping of auditory stimuli: Sequences of sounds that differ only in duration are grouped as iambs (i.e., the most prominent element marks the end of a sequence of sounds), and sequences that differ only in pitch or intensity are grouped as trochees (i.e., the most prominent element marks the beginning of a sequence). In 3 experiments, comprising a familiarization and a test phase, we investigated whether a similar grouping principle is also present in the visual modality. During familiarization, sequences of visual stimuli were repeatedly presented to participants, who were asked to memorize their order of presentation. In the test phase, participants were better at remembering fragments of the familiarization sequences that were consistent with the iambic-trochaic law. Thus, they were better at remembering fragments that had the element with longer duration in final position (iambs) and fragments that had the element with either higher temporal frequency or higher intensity in initial position (trochees), as compared with fragments that were inconsistent with the iambic-trochaic law or that never occurred during familiarization.     

MEMORY PROCESSES IN DELAYED SPATIAL DISCRIMINATIONS: RESPONSE INTENTIONS OR RESPONSE MEDIATION?

Pigeons were trained on a pair-comparison task in which left versus right choices were reinforced following different sequences of two center-key stimuli. Choice accuracy was higher when retention intervals occurred after the entire sequence than when they separated the two stimuli comprising it, and this effect occurred independently of whether the initial and terminal stimuli came from the same or different dimensions. The initial stimulus from the prior trial was a source of proactive interference only in groups for which the retention interval separated the two sequence stimuli. By contrast, differential delay-interval behavior was observed only in groups for which the retention interval followed presentation of the entire sequence. These results indicate that coding processes in delayed discriminations are influenced by the location of the retention interval, and that response mediation affects retention performances if the reinforced choice can be determined prior to the interval.     

Numerosity and rhythmicity in stimulus-response compatibility

When people must respond discriminatively to 1 or 2 stimuli by making 1 or 2 taps of a response key, they initiate the response more rapidly when the correct number of taps matches the number of stimuli (compatible condition) than when it mismatches (incompatible condition; J. O. Miller, S. G. Atkins, & F. Van Nes, 2005). Miller et al. sometimes found an effect of compatibility on response execution time, as reflected in the interresponse intervals between successive taps. The authors report 2 further experiments (N = 8 participants) in which they generalized the numerosity compatibility effects on response-initiation time and interresponse intervals to 2- versus 3-stimulus sequences. In addition, they varied gap length between stimuli to see whether the rhythm of the stimulus would influence that of the response. Weak rhythmicity effects were repeatedly found, but those were too small to suggest a plausible alternative explanation for the numerosity compatibility effect on response-initiation time.     

The role of stimulus-based and response-based spatial information in sequence learning

In 4 experiments, relational structures were independently varied in stimulus and response sequences in a serial reaction time task. Moreover, the use of spatial and symbolic stimuli and responses was varied between experiments. In Experiment 1, spatial stimuli (asterisk locations) triggered spatial responses (keystrokes); in Experiment 2, spatial stimuli triggered symbolic responses (verbal digit naming); in Experiment 3, symbolic stimuli (digits) triggered keystrokes; and in Experiment 4, digits triggered verbal responses. The results showed that there is a remarkably stronger effect of relational structures in spatial sequences than in symbolic sequences, irrespective of whether stimulus or response sequences are concerned. This suggests that learning is particularly effective for sequences of spatial locations. It is argued that spatial learning is a critical determinant for the debate on perceptual and motor learning.     

Design sequences for sensory studies: Achieving balance for carry‐over and position effects

In sequences of human sensory assessments, the response toa stimulus may be influenced by previous stimuli. When investigating this phenomenon experimentally with several types or levels of stimulus, it is useful to have treatment sequences which are balanced for first‐order carry‐over effects. The requirement of balance for each experimental participant leads us to consider sequences of n symbols comprising an initial symbol followed by n ‘blocks’ each containing a permutation of the symbols. These sequences are designed to include all n² ordered pairs of symbols once each, and to have treatment and sequence position effects which are approximately or thogonal. Such sequences were suggested by Finney and Outhwaite (1956) , who were able to find examples for particular values of n. We describe and illustrate acomputer algorithm for systematically enumerating the sequences for those values of n for which they exist. Criteria are proposed for choosing between the sequences according to the nearness to orthogonality of their treatment and position effects.     

Numerosity and Rhythmicity in Stimulus-Response Compatibility

When people must respond discriminatively to 1 or 2 stimuli by making 1 or 2 taps of a response key, they initiate the response more rapidly when the correct number of taps matches the number of stimuli (compatible condition) than when it mismatches (incompatible condition; J. O. Miller, S. G. Atkins, & F. Van Nes, 2005). Miller et al. sometimes found an effect of compatibility on response execution time, as reflected in the interresponse intervals between successive taps. The authors report 2 further experiments (N=8 participants) in which they generalized the numerosity compatibility effects on response-initiation time and interresponse intervals to 2- versus 3-stimulus sequences. In addition, they varied gap length between stimuli to see whether the rhythm of the stimulus would influence that of the response. Weak rhythmicity effects were repeatedly found, but those were too small to suggest a plausible alternative explanation for the numerosity compatibility effect on response-initiation time.     

(Non)words, (non)words, (non)words: evidence for a protolexicon during the first year of life

Previous research with artificial language learning paradigms has shown that infants are sensitive to statistical cues to word boundaries (Saffran, Aslin & Newport, 1996) and that they can use these cues to extract word‐like units (Saffran, 2001). However, it is unknown whether infants use statistical information to construct a receptive lexicon when acquiring their native language. In order to investigate this issue, we rely on the fact that besides real words a statistical algorithm extracts sound sequences that are highly frequent in infant‐directed speech but constitute nonwords. In three experiments, we use a preferential listening paradigm to test French‐learning 11‐month‐old infants' recognition of highly frequent disyllabic sequences from their native language. In Experiments 1 and 2, we use nonword stimuli and find that infants listen longer to high‐frequency than to low‐frequency sequences. In Experiment 3, we compare high‐frequency nonwords to real words in the same frequency range, and find that infants show no preference. Thus, at 11 months, French‐learning infants recognize highly frequent sound sequences from their native language and fail to differentiate between words and nonwords among these sequences. These results are evidence that they have used statistical information to extract word candidates from their input and stored them in a ‘protolexicon’, containing both words and nonwords.     

Memory and learning for visual signals in time and space

Vision is often characterized as a spatial sense, but what does that characterization imply about the relative ease of processing visual information distributed over time rather than over space? Three experiments addressed this question, using stimuli comprising random luminances. For some stimuli, individual items were presented sequentially, at 8 Hz; for other stimuli, individual items were presented simultaneously, as horizontal spatial arrays. For temporal sequences, subjects judged whether each of the last four luminances matched the corresponding luminance in the first four; for spatial arrays, they judged whether each of the right-hand four luminances matched the corresponding left-hand luminance. Overall, performance was far better with spatial presentations, even when the entire spatial array was presented for just tens of milliseconds. Experiment 2 demonstrated that there was no gain in performance from combining spatial and temporal information within a single stimulus. In a final experiment, particular spatial arrays or temporal sequences were made to recur intermittently, interspersed among, non-recurring stimuli. Performance improved steadily as particular stimulus exemplars recurred, with spatial and temporal stimuli being learned at equivalent rates. Logistic regression identified several shortcut strategies that subjects may have exploited while performing our task.     

Part-whole relationships in the processing of small visual patterns

Subjects seem to react to a word faster than they react to a letter within a word. One interpretation is that words are processed holistically; another is that all visual stimuli are processed in terms of components, but that more stimulus information is available for use when the targets are words than when they are letters within words. The results of three experiments indicate that the word or pattern-level advantage occurs even when the stimulus information in the two situations is equated, but if the perceptual arrays cannot be unitized (e.g., consonant sequences), a pattern-level advantage does not occur. In addition, the experiments provide substantial evidence to indicate that if letter arrays cannot be unitized, then they are processed on a componentby-component basis, rather than holistically. Finally, the appropriate definition ofholistic processing is considered.     

Response uncertainty and perceptual difficulty of auditory temporal patterns

Two qualitatively different sounds were used to generate256 different sequences of length8, and these sequences were presented to Ss at a rate of two stimuli per second. These sequences, when repeatedcontinuously,canbe grouped into20 fundame ntally different patterns, each having either2, 4, or8 distinguishably different starting points. Ss were required to listen and to be gin responding (with telegraph keys) in synchrony to the patterns when they were able. The point at which they began responding, the delay before responding, and errors after beginning responding were measured. The response uncertainty (variability of point of response for a given pattern), average delay, and average errors are all highly correlated, indicating that patterns which are easily organized are those which have few alternative modes of organization, and thus can be considered as simple, or good in the Gestalt sense.     

Learning of sensory sequences in cerebellar patients

A possible role of the cerebellum in detecting and recognizing event sequences has been proposed. The present study sought to determine whether patients with cerebellar lesions are impaired in the acquisition and discrimination of sequences of sensory stimuli of different modalities. A group of 26 cerebellar patients and 26 controls matched for age, sex, handedness, musicality, and level of education were tested. Auditory and visual sensory sequences were presented out of different sensory pattern categories (tones with different acoustic frequencies and durations, visual stimuli with different spatial locations and colors, sequential vision of irregular shapes) and different ranges of inter-cue time intervals (fast and slow). Motor requirements were small, with vocal responses and no time restrictions. Perception of visual and acoustic stimuli was generally preserved in patients and controls. The number of errors was significantly higher in the faster tempo of sequence presentation in learning of sequences of tones of different frequencies and in learning of sequences of visual stimuli of different spatial locations and different colors. No difference in tempo between the groups was shown. The total number of errors between the two groups was identical in the sequence conditions. No major disturbances in acquisition or discrimination of various sensory sequences were observed in the group of cerebellar patients. Sequence learning may be impaired only in tasks with significant motor demands.     

The detection and generation of sequences as a key to cerebellar function: experiments and theory

Starting from macroscopic and microscopic facts of cerebellar histology, we propose a new functional interpretation that may elucidate the role of the cerebellum in movement control. The idea is that the cerebellum is a large collection of individual lines (Eccles's "beams": Eccles et al. 1967a) that respond specifically to certain sequences of events in the input and in turn produce sequences of signals in the output. We believe that the sequence-in/sequence-out mode of operation is as typical for the cerebellar cortex as the transformation of sets into sets of active neurons is typical for the cerebral cortex, and that both the histological differences between the two and their reciprocal functional interactions become understandable in the light of this dichotomy. The response of Purkinje cells to sequences of stimuli in the mossy fiber system was shown experimentally by Heck on surviving slices of rat and guinea pig cerebellum. Sequential activation of a row of eleven stimulating electrodes in the granular layer, imitating a "movement" of the stimuli along the folium, produces a powerful volley in the parallel fibers that strongly excites Purkinje cells, as evidenced by intracellular recording. The volley, or "tidal wave," has maximal amplitude when the stimulus moves toward the recording site at the speed of conduction in parallel fibers, and much smaller amplitudes for lower or higher "velocities." The succession of stimuli has no effect when they "move" in the opposite direction. Synchronous activation of the stimulus electrodes also had hardly any effect. We believe that the sequences of mossy fiber activation that normally produce this effect in the intact cerebellum are a combination of motor planning relayed to the cerebellum by the cerebral cortex, and information about ongoing movement, reaching the cerebellum from the spinal cord. The output elicited by the specific sequence to which a "beam" is tuned may well be a succession of well timed inhibitory volleys "sculpting" the motor sequences so as to adapt them to the complicated requirements of the physics of a multijointed system.