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Biomedical subjects

Richard N Aslin

Publications and source records attributed to Richard N Aslin.

At least 19 recordsLinked to original sources
PubMed2007

What's in a look?

The most common behavioral technique used to study infant perception, cognition, language, and social development is some variant of looking time. Since its inception as a reliable method in the late 1950s, a tremendous increase in knowledge about infant competencies has been gained by inferences made from measures of looking time. Here we examine the logic, utility, and future prospects for further gains in our understanding of infant cognition from the use of looking time measures.

Attention↗
PubMed2006

Lexical competition in young children's word learning.

In two experiments, 1.5-year-olds were taught novel words whose sound patterns were phonologically similar to familiar words (novel neighbors) or were not (novel nonneighbors). Learning was tested using a picture-fixation task. In both experiments, children learned the novel nonneighbors but not the novel neighbors. In addition, exposure to the novel neighbors impaired recognition performance on familiar neighbors. Finally, children did not spontaneously use phonological differences to infer that a novel word referred to a novel object. Thus, lexical competition--inhibitory interaction among words in speech comprehension--can prevent children from using their full phonological sensitivity in judging words as novel. These results suggest that word learning in young children, as in adults, relies not only on the discrimination and identification of phonetic categories, but also on evaluating the likelihood that an utterance conveys a new word.

Child Development↗
PubMed2006

Consequences of lexical stress on learning an artificial lexicon.

Four experiments examined effects of lexical stress on lexical access for recently learned words. Participants learned artificial lexicons (48 words) containing phonologically similar items and were tested on their knowledge in a 4-alternative forced-choice (4AFC) referent-selection task. Lexical stress differences did not reduce confusions between cohort items: KAdazu and kaDAzeI were confused with one another in a 4AFC task and in gaze fixations as often as BOsapeI and BOsapaI. However, lexical stress did affect the relative likelihood of stress-initial confusions when words were embedded in running nonsense speech. Words with medial stress, regardless of initial vowel quality, were more prone to confusions than words with initial stress. The authors concluded that non-initial stress, particularly when wor segmentation is difficult, may serve as "noise" that alters lexical learning and lexical access.

Adolescent↗
PubMed2005

Infants are sensitive to within-category variation in speech perception.

Previous research on speech perception in both adults and infants has supported the view that consonants are perceived categorically; that is, listeners are relatively insensitive to variation below the level of the phoneme. More recent work, on the other hand, has shown adults to be systematically sensitive to within category variation [McMurray, B., Tanenhaus, M., & Aslin, R. (2002). Gradient effects of within-category phonetic variation on lexical access, Cognition, 86 (2), B33-B42.]. Additionally, recent evidence suggests that infants are capable of using within-category variation to segment speech and to learn phonetic categories. Here we report two studies of 8-month-old infants, using the head-turn preference procedure, that examine more directly infants' sensitivity to within-category variation. Infants were exposed to 80 repetitions of words beginning with either /b/ or /p/. After exposure, listening times to tokens of the same category with small variations in VOT were significantly different than to both the originally exposed tokens and to the cross-category-boundary competitors. Thus infants, like adults, show systematic sensitivity to fine-grained, within-category detail in speech perception.

Discrimination Learning↗
PubMed2005

Methodological challenges for understanding cognitive development in infants.

Studies of cognitive development in human infants have relied almost entirely on descriptive data at the behavioral level - the age at which a particular ability emerges. The underlying mechanisms of cognitive development remain largely unknown, despite attempts to correlate behavioral states with brain states. We argue that research on cognitive development must focus on theories of learning, and that these theories must reveal both the computational principles and the set of constraints that underlie developmental change. We discuss four specific issues in infant learning that gain renewed importance in light of this opinion.

Adult↗
PubMed2005

Encoding multielement scenes: statistical learning of visual feature hierarchies.

The authors investigated how human adults encode and remember parts of multielement scenes composed of recursively embedded visual shape combinations. The authors found that shape combinations that are parts of larger configurations are less well remembered than shape combinations of the same kind that are not embedded. Combined with basic mechanisms of statistical learning, this embeddedness constraint enables the development of complex new features for acquiring internal representations efficiently without being computationally intractable. The resulting representations also encode parts and wholes by chunking the visual input into components according to the statistical coherence of their constituents. These results suggest that a bootstrapping approach of constrained statistical learning offers a unified framework for investigating the formation of different internal representations in pattern and scene perception.

Adolescent↗
PubMed2004

Learning at a distance II. Statistical learning of non-adjacent dependencies in a non-human primate.

In earlier work we have shown that adults, infants, and cotton-top tamarin monkeys are capable of computing the probability with which syllables occur in particular orders in rapidly presented streams of human speech, and of using these probabilities to group adjacent syllables into word-like units. We have also investigated adults' learning of regularities among elements that are not adjacent, and have found strong selectivities in their ability to learn various kinds of non-adjacent regularities. In the present paper we investigate the learning of these same non-adjacent regularities in tamarin monkeys, using the same materials and familiarization methods. Three types of languages were constructed. In one, words were formed by statistical regularities between non-adjacent syllables. Words contained predictable relations between syllables 1 and 3; syllable 2 varied. In a second type of language, words were formed by statistical regularities between non-adjacent segments. Words contained predictable relations between consonants; the vowels varied. In a third type of language, also formed by regularities between non-adjacent segments, words contained predictable relations between vowels; the consonants varied. Tamarin monkeys were exposed to these languages in the same fashion as adults (21 min of exposure to a continuous speech stream) and were then tested in a playback paradigm measuring spontaneous looking (no reinforcement). Adult subjects learned the second and third types of language easily, but failed to learn the first. However, tamarin monkeys showed a different pattern, learning the first and third type of languages but not the second. These differences held up over multiple replications, using different sounds instantiating each of the patterns. These results suggest differences among learners in the elementary units perceived in speech (syllables, consonants, and vowels) and/or the distance over which such units can be related, and therefore differences among learners in the types of patterned regularities they can acquire. Such studies with tamarins open interesting questions about the perceptual and computational capacities of human learners that may be essential for language acquisition, and how they may differ from those of non-human primates.

Animals↗
PubMed2004

Young children's sensitivity to probabilistic phonotactics in the developing lexicon.

A series of three experiments examined children's sensitivity to probabilistic phonotactic structure as reflected in the relative frequencies with which speech sounds occur and co-occur in American English. Children, ages 212 and 312 years, participated in a nonword repetition task that examined their sensitivity to the frequency of individual phonetic segments and to the frequency of combinations of segments. After partialling out ease of articulation and lexical variables, both groups of children repeated higher phonotactic frequency nonwords more accurately than they did low phonotactic frequency nonwords, suggesting sensitivity to phoneme frequency. In addition, sensitivity to individual phonetic segments increased with age. Finally, older children, but not younger children, were sensitive to the frequency of larger (diphone) units. These results suggest not only that young children are sensitive to fine-grained acoustic-phonetic information in the developing lexicon but also that sensitivity to all aspects of the sound structure increases over development. Implications for the acoustic nature of both developing and mature lexical representations are discussed.

Acoustics↗
PubMed2004

Depth-dependent blur adaptation.

Variations in blur are present in retinal images of scenes containing objects at multiple depth planes. Here we examine whether neural representations of image blur can be recalibrated as a function of depth. Participants were exposed to textured images whose blur changed with depth in a novel manner. For one group of participants, image blur increased as the images moved closer; for the other group, blur increased as the images moved away. A comparison of post-test versus pre-test performances on a blur-matching task at near and far test positions revealed that both groups of participants showed significant experience-dependent recalibration of the relationship between depth and blur. These results demonstrate that blur adaptation is conditioned by 3D viewing contexts.

Adaptation, Ocular↗
PubMed2004

Depth-dependent contrast gain-control.

Contrast adaptation that was limited to a small region of the peripheral retina was induced as observers viewed a multiple depth-plane textured surface. The small region undergoing contrast adaptation was present only in one depth-plane to determine whether contrast gain-control is depth-dependent. After adaptation, observers performed a contrast-matching task in both the adapted and a non-adapted depth-plane to measure the magnitude and spatial specificity of contrast adaptation. Results indicated that contrast adaptation was depth-dependent under full-cue (disparity, linear perspective, texture gradient) conditions; there was a highly significant change in contrast gain in the depth-plane of adaptation and no significant gain change in the unadapted depth-plane. A second experiment showed that under some monocular viewing conditions a similar change in contrast gain was present in the adapted depth-plane despite the absence of disparity information for depth. Two control experiments with no-depth displays showed that contrast adaptation can also be texture- and location-dependent, but the magnitude of these effects was significantly smaller than the depth-dependent effect. These results demonstrate that mechanisms of contrast adaptation are conditioned by 3-D and 2-D viewing contexts.

Adaptation, Ocular↗
PubMed2004

Learning at a distance I. Statistical learning of non-adjacent dependencies.

In earlier work we have shown that adults, young children, and infants are capable of computing transitional probabilities among adjacent syllables in rapidly presented streams of speech, and of using these statistics to group adjacent syllables into word-like units. In the present experiments we ask whether adult learners are also capable of such computations when the only available patterns occur in non-adjacent elements. In the first experiment, we present streams of speech in which precisely the same kinds of syllable regularities occur as in our previous studies, except that the patterned relations among syllables occur between non-adjacent syllables (with an intervening syllable that is unrelated). Under these circumstances we do not obtain our previous results: learners are quite poor at acquiring regular relations among non-adjacent syllables, even when the patterns are objectively quite simple. In subsequent experiments we show that learners are, in contrast, quite capable of acquiring patterned relations among non-adjacent segments-both non-adjacent consonants (with an intervening vocalic segment that is unrelated) and non-adjacent vowels (with an intervening consonantal segment that is unrelated). Finally, we discuss why human learners display these strong differences in learning differing types of non-adjacent regularities, and we conclude by suggesting that these contrasts in learnability may account for why human languages display non-adjacent regularities of one type much more widely than non-adjacent regularities of the other type.

Adult↗
PubMed2004

Distant melodies: statistical learning of nonadjacent dependencies in tone sequences.

Human listeners can keep track of statistical regularities among temporally adjacent elements in both speech and musical streams. However, for speech streams, when statistical regularities occur among nonadjacent elements, only certain types of patterns are acquired. Here, using musical tone sequences, the authors investigate nonadjacent learning. When the elements were all similar in pitch range and timbre, learners acquired moderate regularities among adjacent tones but did not acquire highly consistent regularities among nonadjacent tones. However, when elements differed in pitch range or timbre, learners acquired statistical regularities among the similar, but temporally nonadjacent, elements. Finally, with a moderate grouping cue, both adjacent and nonadjacent statistics were learned, indicating that statistical learning is governed not only by temporal adjacency but also by Gestalt principles of similarity.

Auditory Perception↗
PubMed2003

Probabilistic constraint satisfaction at the lexical/phonetic interface: evidence for gradient effects of within-category VOT on lexical access.

Research in speech perception has been dominated by a search for invariant properties of the signal that correlate with lexical and sublexical categories. We argue that this search for invariance has led researchers to ignore the perceptual consequences of systematic variation within such categories and that sensitivity to this variation may provide an important source of information for integrating information over time in speech perception. Data from a study manipulating VOT continua in words using an eye-movement paradigm indicate that lexical access shows graded sensitivity to within-category variation in VOT and that this sensitivity has a duration sufficient to be useful for information integration. These data support a model in which the perceptual system integrates information from multiple sources and from the surrounding temporal context using probabilistic cue-weighting mechanisms.

Eye Movements↗
PubMed2003

The time course of spoken word learning and recognition: studies with artificial lexicons.

The time course of spoken word recognition depends largely on the frequencies of a word and its competitors, or neighbors (similar-sounding words). However, variability in natural lexicons makes systematic analysis of frequency and neighbor similarity difficult. Artificial lexicons were used to achieve precise control over word frequency and phonological similarity. Eye tracking provided time course measures of lexical activation and competition (during spoken instructions to perform visually guided tasks) both during and after word learning, as a function of word frequency, neighbor type, and neighbor frequency. Apparent shifts from holistic to incremental competitor effects were observed in adults and neural network simulations, suggesting such shifts reflect general properties of learning rather than changes in the nature of lexical representations.

Artificial Intelligence↗
PubMed2003

Bayesian integration of visual and auditory signals for spatial localization.

Human observers localize events in the world by using sensory signals from multiple modalities. We evaluated two theories of spatial localization that predict how visual and auditory information are weighted when these signals specify different locations in space. According to one theory (visual capture), the signal that is typically most reliable dominates in a winner-take-all competition, whereas the other theory (maximum-likelihood estimation) proposes that perceptual judgments are based on a weighted average of the sensory signals in proportion to each signal's relative reliability. Our results indicate that both theories are partially correct, in that relative signal reliability significantly altered judgments of spatial location, but these judgments were also characterized by an overall bias to rely on visual over auditory information. These results have important implications for the development of cue integration and for neural plasticity in the adult brain that enables humans to optimally integrate multimodal information.

Bayes Theorem↗
PubMed2003

Phonological neighbourhoods in the developing lexicon.

Structural analyses of developing lexicons have provided evidence for both children's holistic lexical representations and sensitivity to phonetic segments. In the present investigation, neighbourhood analyses of two children's (age 3;6) expressive lexicons, maternal input, and an adult lexicon were conducted. In addition to raw counts and frequency-weighted counts, neighbourhood size was calculated as the proportion of the lexicon to which each target word is similar, to normalize for vocabulary size differences. These analyses revealed that children's lexicons contain more similar sounding words than previous analyses indicated. Further, neighbourhoods appear denser earlier in development relative to vocabulary size, presumably because children first learn words with more frequent sounds and sound combinations. Neighbourhood density as a proportion of the size of the lexicon then decreases over development as children acquire words with less frequent sounds and sound combinations. These findings suggest that positing fundamentally different lexical representations for children may be premature.

Child↗
PubMed2002

Statistical learning of new visual feature combinations by infants.

The ability of humans to recognize a nearly unlimited number of unique visual objects must be based on a robust and efficient learning mechanism that extracts complex visual features from the environment. To determine whether statistically optimal representations of scenes are formed during early development, we used a habituation paradigm with 9-month-old infants and found that, by mere observation of multielement scenes, they become sensitive to the underlying statistical structure of those scenes. After exposure to a large number of scenes, infants paid more attention not only to element pairs that cooccurred more often as embedded elements in the scenes than other pairs, but also to pairs that had higher predictability (conditional probability) between the elements of the pair. These findings suggest that, similar to lower-level visual representations, infants learn higher-order visual features based on the statistical coherence of elements within the scenes, thereby allowing them to develop an efficient representation for further associative learning.

Association Learning↗