Biology subjects

Fyshe, A.

Publications and source records attributed to Fyshe, A..

4 recordsLinked to original sources

bioRxiv2022

Connecting Covert Attention and Visual Perception to the Spatiotemporal Dynamics of Alpha Band Activity, Cross-Frequency Coupling (CFC), and Functional Connectivity using Multivariate Pattern Analysis (MVPA)

Some evidence suggests that alpha activity is directly related to the baseline firing rate of sensory neurons which alters the probability of responding to a stimulus. Other evidence points to alpha indirectly modulating cortical excitability through its interactions with gamma oscillations. A third possibility is that alpha-based functional connectivity better explains attentional modulation and perceptual responses. To test this, alpha amplitude, CFC, and functional connectivity measures were extracted from EEG data recorded while participants performed a cued orientation perception task. Using pre-target data, the spatiotemporal activity of each metric was submitted to a SVM classifier to determine which activity pattern best distinguished trials with covert attention from trials without. The same metrics were submitted to SVR to find the activity that best predicted task performance. Results indicate the best metric for classifying trials with and without covert attention was alpha amplitude. This indicates that, prior to target onset, alpha amplitude alone is most sensitive to the presence of covert attention. In contrast, none of the metrics were strong predictors of task performance. Overall, our results support the idea that alpha activity is directly related to changes in the baseline firing rate of sensory neurons which changes responsiveness but not performance.

neuroscience↗

bioRxiv2021

Insights into Early Word Comprehension: Tracking the Neural Representations of Word Semantics in Infants.

Infants develop foundational language skills and can understand simple words well before their first birthday. This developmental milestone has been studied primarily using looking time paradigms and Event-Related Potential (ERP) techniques, which provide evidence of word comprehension in the infant brain. While prior research validates the presence of semantic representations of words (word meaning) in infants, it does not tell us about the mental processes involved in retrieving these semantic representations or the content of the representations. To this end, we use a machine learning approach to predict the semantic representations of words using Electroencephalograms of infant brain activity. We explore semantic representations in two groups of infants (9-month-old and 12-month-old) and find significantly above chance decodability of overall word semantics, word animacy, and word phonetics. We compare decodability between the age groups and find significant differences later in the analysis window (around 700-900 ms after word onset), with higher decoding performance in 9-month-olds. Through our analysis, we also observe strong neural representations of word phonetics in the brain data for both age groups, some possibly correlated to word decoding accuracy and others not. Finally, we use the Temporal Generalization Method to show that neural representation of word semantics generalizes across the two infant age groups. Our results on word semantics, phonetics, and animacy provide insights into the evolution of neural representation of single word meaning in infants.

neuroscience↗

bioRxiv2020

Neural representation of words within phrases: Temporal evolution of color-adjectives and object-nouns during simple composition

In language, stored representations of lexical items combine into an infinitude of complex expressions. While the neuroscience of composition has begun to mature, we do not yet understand how the stored representations evolve and morph during composition. New decoding techniques allow us to crack open this very hard question: we can train a model to recognize a representation in one context or time-point and assess its accuracy in another. We combined the decoding approach with magnetoencephalography recorded during a picture naming task to investigate the temporal evolution of noun and adjective representations during speech planning. We tracked word representations as they combined into simple two-word phrases, using single words and two-word lists as non-combinatory controls. We found that nouns were generally more decodable than adjectives, suggesting that noun representations were stronger and/or more consistent across trials than those of adjectives. When training and testing across contexts and times, the representations of isolated nouns were recoverable when those nouns were embedded in phrases, but not so if they were embedded in lists. Adjective representations did not show a similar consistency across isolated and phrasal contexts. Noun representations in phrases also sustained over time in a way that was not observed for any other pairing of word class and context. These findings offer a new window into the temporal evolution and context sensitivity of word representations during composition, revealing a clear asymmetry between adjectives and nouns. The impact of phrasal contexts on the decodability of nouns may be due to the nouns status as head of phrase--an intriguing hypothesis for future research.

neuroscience↗

bioRxiv2016

The Semantics of Adjective Noun Phrases in the Human Brain

As a person reads, the brain performs complex operations to create higher order semantic representations from individual words. While these steps are effortless for competent readers, we are only beginning to understand how the brain performs these actions. Here, we explore semantic composition using magnetoencephalography (MEG) recordings of people reading adjective-noun phrases presented one word at a time. We track the neural representation of semantic information over time, through different brain regions. Our results reveal two novel findings: 1) a neural representation of the adjective is present during noun presentation, but this neural representation is different from that observed during adjective presentation 2) the neural representation of adjective semantics observed during adjective reading is reactivated after phrase reading, with remarkable consistency. We also note that while the semantic representation of the adjective during the reading of the adjective is very distributed, the later representations are concentrated largely to temporal and frontal areas previously associated with composition. Taken together, these results paint a picture of information flow in the brain as phrases are read and understood.

neuroscience↗