Perceptual Learning Paradigm Research Articles

Inter-individual variability in neural response to low doses of LSD

The repeated use of small doses of psychedelics (also referred to as “microdosing”) to facilitate benefits in mental health, cognition, and mood is a trending practice. Placebo-controlled studies however have largely failed to demonstrate strong benefits, possibly because of large inter-individual response variability. The current study tested the hypothesis that effects of low doses of LSD on arousal, attention and memory depend on an individual’s cognitive state at baseline. Healthy participants (N = 53) were randomly assigned to receive repeated doses of LSD (15 mcg) or placebo on 4 occasions divided over 2 weeks. Each treatment condition also consisted of a baseline and a 1-week follow-up visit. Neurophysiological measures of arousal (resting state EEG), pre-attentive processing (auditory oddball task), and perceptual learning and memory (visual long-term potentiation (LTP) paradigm) were assessed at baseline, dosing session 1 and 4, and follow-up. LSD produced stimulatory effects as reflected by a reduction in resting state EEG delta, theta, and alpha power, and enhanced pre-attentive processing during the acute dosing sessions. LSD also blunted the induction of LTP on dosing session 4. Stimulatory effects of LSD were strongest in individuals with low arousal and attention at baseline, while inhibitory effects were strongest in high memory performers at baseline. Decrements in delta EEG power and enhanced pre-attentive processing in the LSD treatment condition were still present during the 1-week follow-up. The current study demonstrates across three cognitive domains, that acute responses to low doses of LSD depend on the baseline state and provides some support for LSD induced neuroadaptations that sustain beyond treatment.

The direction of attention in second language phonological contrast learning.

This study attempted to describe why some individuals are more successful when learning to perceive the sounds of a second language by analyzing the role attention plays in perceptual learning. Fifty-seven monolingual English-speaking adults completed the study. The participants underwent a perceptual learning paradigm presenting the novel contrast, the voicing contrast between Thai /b/ and /p/. The experiment consisted of a 40-item pretest, 480-trial learning phase, and 40-item posttest. Approximately half of the participants (n = 30) were given explicit instruction to listen for the specific contrast prior to the learning phase; other participants were not told the nature of the contrast. The Attention Network Test (ANT) from Fan, McCandliss, Sommer, Raz, and Posner [(2002). J. Cogn. Neurosci. 14(3), 340-347] was used to assess attentional networks. Generalized linear models and linear mixed effect models (LME) were fit to predict the participants' post-test scores based on ANT subscores, experimental group, and learning block (LME only). The results showed a correlation between attentional control and the ability to learn non-native phoneme contrasts regardless of instruction. In addition, there was a positive interaction between attentional control and the provision of explicit instructions during the learning process, such that individuals with high attentional control learned better when they received explicit instruction prior to training.

Hearing is believing: Lexically guided perceptual learning is graded to reflect the quantity of evidence in speech input

There is wide variability in the acoustic patterns that are produced for a given linguistic message, including variability that is conditioned on who is speaking. Listeners solve this lack of invariance problem, at least in part, by dynamically modifying the mapping to speech sounds in response to structured variation in the input. Here we test a primary tenet of the ideal adapter framework of speech adaptation, which posits that perceptual learning reflects the incremental updating of cue-sound mappings to incorporate observed evidence with prior beliefs. Our investigation draws on the influential lexically guided perceptual learning paradigm. During an exposure phase, listeners heard a talker who produced fricative energy ambiguous between /ʃ/ and /s/. Lexical context differentially biased interpretation of the ambiguity as either /s/ or /ʃ/, and, across two behavioral experiments (n = 500), we manipulated the quantity of evidence and the consistency of evidence that was provided during exposure. Following exposure, listeners categorized tokens from an ashi – asi continuum to assess learning. The ideal adapter framework was formalized through computational simulations, which predicted that learning would be graded to reflect the quantity, but not the consistency, of the exposure input. These predictions were upheld in human listeners; the magnitude of the learning effect monotonically increased given exposure to four, 10, or 20 critical productions, and there was no evidence that learning differed given consistent versus inconsistent exposure. These results (1) provide support for a primary tenet of the ideal adapter framework, (2) establish quantity of evidence as a key determinant of adaptation in human listeners, and (3) provide critical evidence that lexically guided perceptual learning is not a binary outcome. In doing so, the current work provides foundational knowledge to support theoretical advances that consider perceptual learning as a graded outcome that is tightly linked to input statistics in the speech stream.

Exposure to multisensory and visual static or moving stimuli enhances processing of nonoptimal visual rhythms

Research has shown that visual moving and multisensory stimuli can efficiently mediate rhythmic information. It is possible, therefore, that the previously reported auditory dominance in rhythm perception is due to the use of nonoptimal visual stimuli. Yet it remains unknown whether exposure to multisensory or visual-moving rhythms would benefit the processing of rhythms consisting of nonoptimal static visual stimuli. Using a perceptual learning paradigm, we tested whether the visual component of the multisensory training pair can affect processing of metric simple two integer-ratio nonoptimal visual rhythms. Participants were trained with static (AVstat), moving-inanimate (AVinan), or moving-animate (AVan) visual stimuli along with auditory tones and a regular beat. In the pre- and posttraining tasks, participants responded whether two static-visual rhythms differed or not. Results showed improved posttraining performance for all training groups irrespective of the type of visual stimulation. To assess whether this benefit was auditory driven, we introduced visual-only training with a moving or static stimulus and a regular beat (Vinan). Comparisons between Vinan and Vstat showed that, even in the absence of auditory information, training with visual-only moving or static stimuli resulted in an enhanced posttraining performance. Overall, our findings suggest that audiovisual and visual static or moving training can benefit processing of nonoptimal visual rhythms.

Auditory perceptual learning in autistic adults.

The automatic retuning of phoneme categories to better adapt to the speech of a novel talker has been extensively documented across various (neurotypical) populations, including both adults and children. However, no studies have examined auditory perceptual learning effects in populations atypical in perceptual, social, and language processing for communication, such as populations with autism. Employing a classic lexically-guided perceptual learning paradigm, the present study investigated perceptual learning effects in Australian English autistic and non-autistic adults. The findings revealed that automatic attunement to existing phoneme categories was not activated in the autistic group in the same manner as for non-autistic control subjects. Specifically, autistic adults were able to both successfully discern lexical items and to categorize speech sounds; however, they did not show effects of perceptual retuning to talkers. These findings may have implications for the application of current sensory theories (e.g., Bayesian decision theory) to speech and language processing by autistic individuals. LAY SUMMARY: Lexically guided perceptual learning assists in the disambiguation of speech from a novel talker. The present study established that while Australian English autistic adult listeners were able to successfully discern lexical items and categorize speech sounds in their native language, perceptual flexibility in updating speaker-specific phonemic knowledge when exposed to a novel talker was not available. Implications for speech and language processing by autistic individuals as well as current sensory theories are discussed.

Mechanisms Underlying Directional Motion Processing and Form-Motion Integration Assessed with Visual Perceptual Learning.

Dynamic Glass patterns (GPs) are visual stimuli commonly employed to study form–motion interactions. There is brain imaging evidence that non-directional motion induced by dynamic GPs and directional motion induced by random dot kinematograms (RDKs) depend on the activity of the human motion complex (hMT+). However, whether dynamic GPs and RDKs rely on the same processing mechanisms is still up for dispute. The current study uses a visual perceptual learning (VPL) paradigm to try to answer this question. Identical pre- and post-tests were given to two groups of participants, who had to discriminate random/noisy patterns from coherent form (dynamic GPs) and motion (RDKs). Subsequently, one group was trained on dynamic translational GPs, whereas the other group on RDKs. On the one hand, the generalization of learning to the non-trained stimulus would indicate that the same mechanisms are involved in the processing of both dynamic GPs and RDKs. On the other hand, learning specificity would indicate that the two stimuli are likely to be processed by separate mechanisms possibly in the same cortical network. The results showed that VPL is specific to the stimulus trained, suggesting that directional and non-directional motion may depend on different neural mechanisms.

Cents and Shenshibility: The role of reward in talker-specific phonetic recalibration

We, as listeners, encounter many challenges during speech comprehension that extend far beyond resolving ambiguities in the acoustic phonetic signal. An understudied component of naturalistic speech comprehension is how motivated a listener is to attend to various aspects of the speech signal. This includes, when listening to multiple novel talkers, whether we give talkers equal attention when adapting to their idiosyncratic productions. We asked if listener adaptation is influenced by an external reward that is intended to bias attention towards one talker versus the other. In a lexically guided perceptual learning paradigm, participants heard two talkers of different genders—“Jane” and “Austin”—with idiosyncratic productions of the /s/ and /ʃ/ fricatives. Participants were more likely to receive a small monetary reward for one talker than the other following correct responses during a phoneme-monitoring cover task. We hypothesized that participants would show greater phonetic recalibration for the more-rewarded talker than the less-rewarded talker; however, our results indicate that external reward may undermine learning for both talkers. The role of reward and motivation in talker-specific phonetic recalibration raises interesting questions for how these domain-general factors influence language processing more broadly.

Sleep-Dependent Facilitation of Visual Perceptual Learning Is Consistent with a Learning-Dependent Model

How sleep leads to offline performance gains in learning remains controversial. A use-dependent model assumes that sleep processing leading to performance gains occurs based on general cortical usage during wakefulness, whereas a learning-dependent model assumes that this processing is specific to learning. Here, we found evidence that supports a learning-dependent model in visual perceptual learning (VPL) in humans (both sexes). First, we measured the strength of spontaneous oscillations during sleep after two training conditions that required the same amount of training or visual cortical usage; one generated VPL (learning condition), while the other did not (interference condition). During a post-training nap, slow-wave activity (SWA) and sigma activity during non-rapid eye movement (NREM) sleep and theta activity during REM sleep were source localized to the early visual areas using retinotopic mapping. Inconsistent with a use-dependent model, only in the learning condition, sigma and theta activity, not SWA, increased in a trained region-specific manner and correlated with performance gains. Second, we investigated the roles of occipital sigma and theta activity during sleep. Occipital sigma activity during NREM sleep was significantly correlated with performance gains in presleep learning; however, occipital theta activity during REM sleep was correlated with presleep learning stabilization, shown as resilience to interference from postsleep learning in a trained region-specific manner. Occipital SWA was not associated with offline performance gains or stabilization. These results demonstrate that sleep processing leading to performance gains is learning dependent in VPL and involves occipital sigma and theta activity during sleep.SIGNIFICANCE STATEMENTThe present study shows strong evidence that could help resolve the long-standing controversy surrounding sleep processing that strengthens learning (performance gains). There are two conflicting models. A use-dependent model assumes that sleep processing leading to performance gains occurs because of general cortical usage during wakefulness, whereas a learning-dependent model assumes that processing occurs specifically for learning. Using visual perceptual learning and interference paradigms, we found that processing did not take place after general cortical usage. Moreover, sigma activity during non-rapid eye movement (REM) sleep and theta activity during REM sleep in occipital areas were found to be involved in processing, which is consistent with the learning-dependent model and not the use-dependent model. These results support the learning-dependent model.

Assessing the functions underlying learning using by-trial and by-participant models: Evidence from two visual perceptual learning paradigms.

Inferred mechanisms of learning, such as those involved in improvements resulting from perceptual training, are reliant on (and reflect) the functional forms that models of learning take. However, previous investigations of the functional forms of perceptual learning have been limited in ways that are incompatible with the known mechanisms of learning. For instance, previous work has overwhelmingly aggregated learning data across learning participants, learning trials, or both. Here we approach the study of the functional form of perceptual learning on the by-person and by-trial levels at which the mechanisms of learning are expected to act. Each participant completed one of two visual perceptual learning tasks over the course of two days, with the first 75% of task performance using a single reference stimulus (i.e., “training”) and the last 25% using an orthogonal reference stimulus (to test generalization). Five learning functions, coming from either the exponential or the power family, were fit to each participant's data. The exponential family was uniformly supported by Bayesian Information Criteria (BIC) model comparisons. The simplest exponential function was the best fit to learning on a texture oddball detection task, while a Weibull (augmented exponential) function tended to be the best fit to learning on a dot-motion discrimination task. The support for the exponential family corroborated previous by-person investigations of the functional form of learning, while the novel evidence supporting the Weibull learning model has implications for both the analysis and the mechanistic bases of the learning.

Stimulus onset asynchrony effects on perceptual learning

Listeners use lexical knowledge to guide the perception of phonetically ambiguous speech sounds and for retuning phonetic category boundaries. While phonetic ambiguity has many sources, diachronic sound changes represent a more systematic form of phonetic variation. Sound changes may neutralize the phonetic and phonological contrast between two lexical competitors, rendering lexical knowledge in perceptual learning paradigms an unreliable scaffold for boundary retuning, particularly in languages with a high proportion of monosyllabic lexical items (e.g., Cantonese). We present pilot results of an auditory-object-to-picture matching task for perceptual learning of English vowels in monosyllabic words. Seven-step [æ]-[ɑ] continua were created for three minimal pairs (e.g., “gnat”—“knot”). Images corresponding to the real word endpoints were presented at three different stimulus onset asynchrony (SOA) intervals: −250, 0, +250 ms. Participants responded as to whether the visual image matched the auditory token. Preliminary findings indicate that listeners deem the auditory token and picture a congruent match at higher proportions in the 0 ms SOA condition. Our future work analyzes the subsequent learning in response to this exposure method and uses this SOA in a Cantonese perceptual learning study focused on adaptation to lexical tone variation.

Grating orientation task trial numbers for short- and long-term tactile discrimination learning

Perceptual learning generally improves with training intensity, but the number of training trials sufficient for transient and long-term improvement in tactile grating orientation task (GOT) discrimination has not been systematically studied. To define reliable trial numbers for tactile discrimination learning, we compared tactile orientation discrimination performance of the right-finger following 200 and 400 training trials. Fifty-one neurologically healthy subjects were recruited. Tactile spatial acuity for orientation (parallel or orthogonal to the long axis of the finger) across different grating frequencies was assessed before, immediately after, 30 min after, and 24 h after sessions consisting of 200 training trials (50/block × 4 blocks), 400 training trials (50/block × 8 blocks), or no training (sham control). Both the 200- and 400-trial training conditions reduced the grating orientation discrimination threshold at 24 h after training. In contrast, the control condition had no effect on the grating orientation discrimination threshold. There was a negative correlation between the baseline grating orientation discrimination threshold and training-induced change in threshold (improvement) following both 200 and 400 trials. Fewer GOT trials (200) substantially prolong tactile discrimination learning, presumably by promoting the consolidation of the underlying neuroplastic mechanisms. In this widely used perceptual learning paradigm, 200 and 400 training trials appear effective for inducing short-term and long-term perceptual memory.

A Gradient of Sharpening Effects by Perceptual Prior across the Human Cortical Hierarchy.

Prior knowledge profoundly influences perceptual processing. Previous studies have revealed consistent suppression of predicted stimulus information in sensory areas, but how prior knowledge modulates processing higher up in the cortical hierarchy remains poorly understood. In addition, the mechanism leading to suppression of predicted sensory information remains unclear, and studies thus far have revealed a mixed pattern of results in support of either the "sharpening" or "dampening" model. Here, using 7T fMRI in humans (both sexes), we observed that prior knowledge acquired from fast, one-shot perceptual learning sharpens neural representation throughout the ventral visual stream, generating suppressed sensory responses. In contrast, the frontoparietal and default mode networks exhibit similar sharpening of content-specific neural representation, but in the context of unchanged and enhanced activity magnitudes, respectively: a pattern we refer to as "selective enhancement." Together, these results reveal a heretofore unknown macroscopic gradient of prior knowledge's sharpening effect on neural representations across the cortical hierarchy.SIGNIFICANCE STATEMENT A fundamental question in neuroscience is how prior knowledge shapes perceptual processing. Perception is constantly informed by internal priors in the brain acquired from past experiences, but the neural mechanisms underlying this process are poorly understood. To date, research on this question has focused on early visual regions, reporting a consistent downregulation when predicted stimuli are encountered. Here, using a dramatic one-shot perceptual learning paradigm, we observed that prior knowledge results in sharper neural representations across the cortical hierarchy of the human brain through a gradient of mechanisms. In visual regions, neural responses tuned away from internal predictions are suppressed. In frontoparietal regions, neural activity consistent with priors is selectively enhanced. These results deepen our understanding of how prior knowledge informs perception.

Comparing methods of category learning: Classification versus feature inference

Categories have at least two main functions: classification of instances and feature inference. Classification involves assigning an instance to a category, and feature inference involves predicting a feature for a category instance. Correspondingly, categories can be learned in two distinct ways, by classification and feature inference. A typical difference between these in the perceptual category learning paradigm is the presence of the category label as part of the stimulus in feature inference learning and not in classification learning. So we hypothesized a label-induced rule-bias in feature inference learning compared to classification and evaluated it on an important starting point in the field for category learning – the category structures from Shepard, Hovland, and Jenkins (Psychological Monographs: General and Applied, 75(13), 1-42, 1961). They classically found that classification learning of structures consistent with more complex rules resulted in poorer learning. We compared feature inference learning of these structures with classification learning and found differences between the learning tasks supporting the label-bias hypothesis in terms of an emphasis on label-based rules in feature inference. Importantly, participants’ self-reported rules were largely consistent with their task performance and indicated the preponderance of rule representation in both tasks. So, while the results do not support a difference in the kind of representation for the two learning tasks, the presence of category labels in feature inference tended to focus rule formation. The results also highlight the specialized nature of the classic Shepard et al. (1961) stimuli in terms of being especially conducive to the formation of compact verbal rules.

An investigation of far and near transfer in a gamified visual learning paradigm.

After training, visual perceptual learning improvements are mostly constrained to the trained stimulus feature and retinal location. The aim of this study is to construct an integrated paradigm where the visual learning happens in a more natural context and in parallel for multiple stimulus types, and to test the generalization of learning-related improvements towards untrained features, locations, and more general cognitive domains. Half the subjects were trained with a gamified perceptual learning paradigm for ten hours, which consisted of an orientation discrimination task and a novel object categorization task embedded in a three-dimensional maze. A second group of subjects, an active control group, played ten hours of Candy Crush Saga. Before and after training, all subjects completed a ‘near transfer’ orientation discrimination and novel object categorization task, as well as a set of ‘far transfer’ general cognitive and attentional tasks. During the perceptual learning tasks, two different stimulus features and two retinal location pairs were assessed in each task. For the experimental group, one stimulus feature and retinal location pair was trained, whilst the other one remained untrained. Both features and location pairs were untrained in the control group. Far transfer did occur in some domains across all subjects irrespective of the training regimen (i.e. executive functioning, mental rotation performance, and multitask performance and speed). Near transfer was present in both groups, however only more pronounced for one particular task in the experimental group, namely novel object categorization. To conclude, all but one near transfer task did not generalize more than the control group.

The Goldilocks Zone of Perceptual Learning

Background/Aims: Lexically guided perceptual learning in speech is the updating of linguistic categories based on novel input disambiguated by the structure provided in a recognized lexical item. We test the range of variation that allows for perceptual learning by presenting listeners with items that vary from subtle within-category variation to fully remapped cross-category variation. Methods: Experiment 1 uses a lexically guided perceptual learning paradigm with words containing noncanonical /s/ realizations from s/ʃ continua that correspond to “typical,” “ambiguous,” “atypical,” and “remapped” steps. Perceptual learning is tested in an s/ʃ categorization task. Experiment 2 addresses listener sensitivity to variation in the exposure items using AX discrimination tasks. Results: Listeners in experiment 1 showed perceptual learning with the maximally ambiguous tokens. Performance of listeners in experiment 2 suggests that tokens which showed the most perceptual learning were not perceptually salient on their own. Conclusion: These results demonstrate that perceptual learning is enhanced with maximally ambiguous stimuli. Excessively atypical pronunciations show attenuated perceptual learning, while typical pronunciations show no evidence for perceptual learning. AX discrimination illustrates that the maximally ambiguous stimuli are not perceptually unique. Together, these results suggest that perceptual learning relies on an interplay between confidence in phonetic and lexical predictions and category typicality.

Sensory noise increases metacognitive efficiency.

Metacognitive efficiency quantifies people's ability to introspect into their own decision making relative to their ability to perform the primary task. Despite years of research, it is still unclear how visual metacognitive efficiency can be manipulated. Here, we show that a hierarchical model of confidence generation makes a counterintuitive prediction: Higher sensory noise should increase metacognitive efficiency. The reason for this is that hierarchical models assume that although the primary decision is corrupted only by sensory noise, the confidence judgment is corrupted by both sensory and metacognitive noise. Therefore, increasing sensory noise has a smaller negative influence on the confidence judgment than on the perceptual decision, resulting in increased metacognitive efficiency. To test this prediction, we used a perceptual learning paradigm to decrease sensory noise. In Experiment 1, 7 days of training led to a significant decrease in sensory noise and a corresponding decrease in metacognitive efficiency. Experiment 2 showed the same effect in a brief 97-trial learning for each of 2 different tasks. Finally, in Experiment 3, we combined increasingly dissimilar stimulus contrasts to create conditions with higher sensory noise and observed a corresponding increase in metacognitive efficiency. Our findings demonstrate the existence of a robust positive relationship between across-trial sensory noise and metacognitive efficiency. These results could not be captured by a standard model in which decision and confidence judgments are made based on the same underlying information. Thus, our study provides direct evidence for the existence of metacognitive noise that corrupts confidence but not the perceptual decision. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Specificity and generalization in perceptual adaptation to systematic variation in speech

A signature problem in our understanding of spoken language processing is listeners’ perceptual constancy in the face of considerable variability in the instantiation of linguistic form. Abundant evidence now suggests that listeners are sensitive to the fine-grained structure of linguistic units that signal differences among talkers and track and adapt to this structure during the perception of speech. This talk will present data from a perceptual learning paradigm addressing both the constraints and flexibility of speech perceptual mechanisms. The aim was to address the degree to which exposure to variation in and expectations about talker- and group-specific attributes influence the degree of specificity and generalization in the perceptual adaptation process. Listeners were exposed to talker-dependent variation in a linguistic form, and expectations about talker characteristics were manipulated. The results suggest that listeners dynamically adapt to and encode systematic changes in the linguistic category structure as a function of expectation and appear to flexibly integrate talker- and group-dependent sources of variation into linguistic representation and processing.A signature problem in our understanding of spoken language processing is listeners’ perceptual constancy in the face of considerable variability in the instantiation of linguistic form. Abundant evidence now suggests that listeners are sensitive to the fine-grained structure of linguistic units that signal differences among talkers and track and adapt to this structure during the perception of speech. This talk will present data from a perceptual learning paradigm addressing both the constraints and flexibility of speech perceptual mechanisms. The aim was to address the degree to which exposure to variation in and expectations about talker- and group-specific attributes influence the degree of specificity and generalization in the perceptual adaptation process. Listeners were exposed to talker-dependent variation in a linguistic form, and expectations about talker characteristics were manipulated. The results suggest that listeners dynamically adapt to and encode systematic changes in the linguistic cate...

Do social preferences matter in lexical retuning?

In perceiving spoken language, listeners not only recognize and comprehend the intended meaning of the speaker’s words and phrases; they also assess the social dimensions of the speaker. In the present study, we ask whether perceptual learning — a process by which listeners adapt to novel pronunciations — is modulated by listeners’ social preferences. To this end, we use a novel accent exhibiting a back vowel lowering chain shift in pleasant and unpleasant conditions in a lexically guided perceptual learning paradigm to test whether listeners adapt less to the unpleasant guise. Experiment 1 confirms that listeners disprefer the unpleasant guise. Using a lexical decision task as a measure of lexical adaptation, Experiment 2 indicates that listeners in the pleasant and unpleasant guises learned the back vowel shift compared to listeners in a control group. These results suggest that exposure to a voice with lower social prestige does not inhibit lexical adaptation.

Nonnative implicit phonetic training in multiple reverberant environments

Speech intelligibility is adversely affected by reverberation, particularly when listening to a foreign language. However, little is known about how phonetic learning is affected by room acoustics. This study investigated how room reverberation impacts the acquisition of novel phonetic categories during implicit training in virtual environments. Listeners were trained to distinguish a difficult nonnative dental-retroflex contrast in phonemes presented either in a fixed room (anechoic or reverberant) or in multiple anechoic and reverberant spaces typical of everyday listening. Training employed a videogame in which phonetic stimuli were paired with rewards delivered upon successful task performance, in accordance with the task-irrelevant perceptual learning paradigm. Before and after training, participants were tested using familiar and unfamiliar speech tokens, speakers, and rooms. Implicit training performed in multiple rooms induced learning, while training in a single environment did not. The multiple-room training improvement generalized to untrained rooms and tokens, but not to untrained voices. These results show that, following implicit training, nonnative listeners can overcome the detrimental effects of reverberation and that exposure to sounds in multiple reverberant environments during training enhances implicit phonetic learning rather than disrupting it.

Perceptual-learning evidence for inter-onset-interval- and frequency-specific processing of fast rhythms.

Rhythm is fundamental to music and speech, yet little is known about how even simple rhythmic patterns are processed. Here we investigated the processing of isochronous rhythms in the short inter-onset-interval (IOI) range (IOIs < 250-400 ms) using a perceptual-learning paradigm. Trained listeners (n=8) practiced anisochrony detection with a 100-ms IOI marked by 1-kHz tones, 720 trials per day for 7 days. Between pre- and post-training tests, trained listeners improved significantly more than controls (no training; n=8) on the anisochrony-detection condition that the trained listeners practiced. However, the learning on anisochrony detection did not generalize to temporal-interval discrimination with the trained IOI (100 ms) and marker frequency (1 kHz) or to anisochrony detection with an untrained marker frequency (4 kHz or variable frequency vs. 1 kHz), and generalized negatively to anisochrony detection with an untrained IOI (200 ms vs. 100 ms). Further, pre-training thresholds were correlated among nearly all of the conditions with the same IOI (100-ms IOIs), but not between conditions with different IOIs (100-ms vs. 200-ms IOIs). Thus, it appears that some task-, IOI-, and frequency-specific processes are involved in fast-rhythm processing. These outcomes are most consistent with a holistic rhythm-processing model in which a holistic "image" of the stimulus is compared to a stimulus-specific template.