Using fMRI to Explore the Neural Basis of Anticipation After Implicit Distributional Learning

Danlei Chen, Carol Jew, Benjamin Zinszer, and Rajeev Raizada

Distributional learning research has established that humans can track the frequencies of sequentially presented stimuli in order to infer the probabilities of upcoming events (e.g., Hasher & Zacks, 1984). We hypothesize that as people learn this frequency information, probabilistically weighted representations of the next stimulus are activated in the brain prior to each trial. We present behavioral evidence that these weighted representations are measurable in the response time of the subsequent trial, and we propose a further experiment to directly test the neural hypothesis. In the behavioral experiment, twelve adult participants viewed photographs of faces, tools, and buildings while performing a simple classification task. Each of these categories reliably evokes stronger responses in specific sets of brain areas compared to other categories (Chao & Martin, 2000; Epstein & Kanwisher, 1998; Kanwisher, McDermott, & Chun, 1997), allowing us to measure the intensity of brain activity separately and in parallel for each category in the MRI scanner. The frequency of each category (60%, 30%, 10%) was counterbalanced across six different frequency distributions. Using a two-way (Frequency-by-Category) linear mixed-effects model, we compared response times for the stimuli in each distribution to see whether the anticipation of a more frequent category reduced the response time. Response times significantly decreased with greater frequencies (t(6123) = -7.289, p < .0005), indicating that participants anticipated the stimuli proportional to the probability of the category and thereby reduced response times for the more frequent categories. With this evidence of probabilistic anticipatory representations, we are now testing this effect using functional MRI. We hypothesize that anticipation of a category will evoke activity in category-specific regions proportional to the probability of that category. If the neuroimaging results are in line with this hypothesis, they will suggest that learned distributional information produces probabilistically weighted representations of possible outcomes.

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Center-Embedded Sequence Learning In Children And Non-Human Primates

Abigail Haslinger, Stephen Ferrigno, Steven T. Piantadosi, and Jessica F. Cantlon

Recursion is a computational method that embeds elements inside one another, allowing for long-range relations in a sequence. It is important for a wide variety of human skills, including language, counting, and motor control. To date there has been no conclusive evidence that non-human animals can use center-embedded recursion, the type of recursion necessary for language acquisition. This has led some researchers to hypothesize that it is a uniquely human skill and possibly the limiting factor of human language ability. Here we investigate whether monkeys (rhesus macaques) and children (age 3-5 yrs.) can learn to apply center-embedded recursion in a sequencing task. Subjects were given a task in which they had to touch sets of pictures of brackets in recursive orders, e.g. [ < > ]. We then tested whether subjects could transfer this center-embedded strategy to novel stimuli. We found that children naturally use center-embedded recursion to order novel lists. This suggests that mastery of this task, and thus mastery of a component of human grammar, comes easily to children and develops very early in childhood. Although monkeys did not use center-embedded recursion at first, with additional training, they were capable of learning to use a center-embedded strategy and transfer this skill to novel stimuli. This suggests that center-embedded recursion is not a uniquely human ability and is therefore not likely the limiting factor of language.

No Natural Gender Differences in Children’s Earliest Quantitative Abilities

Kelsey Csumitta and Jessica Cantlon

Despite advances in gender equality within our society, men continue to be overrepresented in math-related careers. If there are “natural” differences in math ability between young boys and girls, these differences may impact later academic and career choices. Although some research has found that boys outperform girls on tests of math achievement in school, cultural influences may be contributing to these differences. Here we examined children’s quantitative processing abilities during early childhood prior to and during the first few years of formal school to provide data on whether and how early gender differences emerge in childhood. Over 400 children between 2 and 7 years were tested across two testing sites. First, we compared the performance of boys and girls on core numerosity perception during infancy and childhood and found that boys and girls performed similarly. Next, we compared boys and girls on verbal counting and knowledge of number word meanings during preschool. Boys and girls demonstrated similar levels of knowledge of number word meanings, but boys showed a slight advantage on culturally-learned memorization. Finally, we compared boys and girls on school-based tests of math achievement during the first few years of formal schooling. Boys and girls performed equally on mathematical concepts that draw on untrained, acquired knowledge, but boys performed slightly better on questions that rely on concepts that are formally taught in school. None of the differences between boys and girls approached one standard deviation. Overall the data show no intrinsic early childhood gender differences in quantitative reasoning, but some negligible gender differences in quantitative concepts that are culturally trained. This suggests that cultural influences may account for the gender discrepancy seen in math-related careers.

Generalized Adaptation to Novel Foreign Accents

Emily Simon, Lauren Oey, Crystal Lee, T. Florian Jaeger, and Xin Xie

Technology has made the world an increasingly interconnected sphere– one in which conversations can occur seamlessly while speakers sit oceans apart. However, with increasing globalization comes increasing demands on listeners to comprehend extensive variability in speech, particularly that of foreign-accented speakers. Nevertheless, evidence suggests that listeners rapidly adapt to accented speech – across varying speaker background, differing intelligibility and relatively brief exposures (Clarke & Garrett, 2004; Bradlow & Bent, 2008; Sidaras et al., 2009). After further exposure, listeners can generalize such adaptation to novel speakers with whom a listener has not previously interacted (Bradlow & Bent, 2008; Baese-Berk et al., 2013). The scope of this generalization, as well as its underlying mechanism, are still unknown. This is largely due to the inherent difficulties of measuring variability within and across speakers quantitatively. We examined generalizability of adaptation to accented speech in cases of exposure to multiple foreign accents. Using an online crowdsourcing paradigm, we will measure listener’s transcription accuracy after exposure to accented speech to assess generalized adaptation ability. During Exposure, listeners are assigned to one of three listening conditions; either 5 speakers of native English, 5 speakers of Mandarin-accented, or 5 speakers of varying language backgrounds (Korean, Thai, Hindi, Russian and Mandarin). After exposure, all listeners will be tested on a novel speaker of a familiar accent, and critically, a novel speaker of a novel accent. We hypothesize that transcription accuracy of novel foreign-accented utterances will be greatest in the case that listeners are exposed to the most systematic variability in accented speech. Under this assumption, we predict that listeners exposed to multiple foreign accents will perform best when tested on a novel accent.

Learning Adjective Meanings Through Variable Exemplars

Crystal Lee and Chigusa Kurumada

How have we learned the meaning of words like ‘full’ or ‘straight’? As adults, we know ‘full’ means ‘containing as much as possible without spilling over’. However, young learners often observe examples where ‘full’ is used to describe objects or situations that deviate from the prototypical definition, despite being contextually appropriate. e.g., a ‘full’ cup could be 90% full when transporting drinks. In fact, Syrett et al. (2010) found contrasting comprehension of absolute gradable adjectives (e.g., full, straight) between children and adults. When asked to give ‘the full cup’ with one 90% full cup and one 70% full cup present, four-year-olds were more willing to pass the 90% full cup. Contrastingly, adults were more likely to say that neither is ‘full’. We hypothesize that accumulated experiences allow adults to account for contextual contributions to word meaning: a 90% full cup is deemed full in an appropriate context (e.g., transporting drinks); otherwise any deviation from the prototypical meaning invalidates an instance to be judged ‘full’. We test this hypothesis by teaching adult subjects a novel gradable adjective; ‘pelty’ roughly meaning ‘tight-fitting’. 60 Subjects are randomly assigned either to With- or Without-context Condition. In Exposure, subjects watch 12 videos exemplifying the word use of objects that are tight-fitting to a varying degree. Those in the With-context condition receives contextual justification (e.g. A moderately tight-fitting shoe is still ‘pelty’ because it has to be worn with a thick sock) and those in the Without-context condition do not. In Test, participants see two novel objects (one 90% pelty and one 70% pelty) and a ‘neither’ option. We predict that subjects in the With-context condition, just as adult subjects in Syrett et al. (2010), would be more willing to select ‘neither’ than those in the Without-context condition.

Contextual Factors in Child Adjective Comprehension

Wesley Orth, Amanda Pogue, and Chigusa Kurumada

This research investigates preschoolers’ understanding of adjectives (e.g., big, clean, metal). While adjectives are part of very basic vocabulary acquired early in development, it is not clear whether children’s conceptual understanding of them is equivocal to that of adults. In particular, I am interested in how they acquire subtle meaning differences across adjectives. Some adjectives require a listener to reason about other objects in order to verify that they are true (e.g., to say a cat is big, one needs to know how large cats usually are), whereas others do not (e.g., to say a cat is striped, one needs to know if that cat has at least one stripe). I created a guessing game to directly compare young children and adults in their comprehension of various adjective types. 16 preschoolers and 20 adults were asked to match a description of an object a card; either a face-up or face-down card. There were three trial types: 1) adjectives that require a comparison class (e.g., big), 2) adjectives that are binary in meaning and do not require a comparison class (e.g., striped), and 3) adjectives that denote a property of the noun (e.g., metal). Participants may or may not flip the face-down card before making a match, the likelihood of which tells us whether they thought a given adjective requires a comparison class. The results show that adults seek out comparative information for the type 1 adjectives but not other adjectives (60%, 11.25%, 9.16% respectively), whereas children seek out less comparative information when necessary, yet still show a similar pattern (35%, 17.5%, 20%). I conclude that children’s understanding of these types of adjectives is qualitatively similar to adults’ while there is a quantitative difference between them. I am currently running a follow up experiment to investigate the nature of the difference.