Research
My research focuses on how people understand speech. I’m interested in how understanding speech influences our perception of low-level acoustic input and vice versa. I am particularly interested in how learning processes, such as discriminative error-driven learning, are involved in speech comprehension and the neural underpinnings of prediction, speech perception and learning. I'm also interested in eye movements as a window onto the cogntive processes involved in speech perception and reading.
The PERCEPtual span is DYNAMically adjusted in response to FOVeal load by Beginning READERS
Johannes M. Meixner, Jessie S. Nixon & Jochen Laubrock
Journal of Experimental Psychology: General, 2022
The perceptual span describes the size of the visual field from which information is obtained during a fixation in reading. Its size depends on characteristics of writing system and reader, but—according to the foveal load hypothesis—it is also adjusted dynamically as a function of lexical processing difficulty. Using the moving window paradigm to manipulate the amount of preview, here we directly test whether the perceptual span shrinks as foveal word difficulty increases....
We computed the momentary size of the span from word-based eye-movement measures as a function of foveal word frequency, allowing us to separately describe the perceptual span for information affecting spatial saccade targeting and temporal saccade execution. First fixation duration and gaze duration on the upcoming (parafoveal) word N + 1 were significantly shorter when the current (foveal) word N was more frequent. We show that the word frequency effect is modulated by window size. Fixation durations on word N + 1 decreased with high-frequency words N, but only for large windows, that is, when sufficient parafoveal preview was available. This provides strong support for the foveal load hypothesis. To investigate the development of the foveal load effect, we analyzed data from three waves of a longitudinal study on the perceptual span with German children in Grades 1 to 6. Perceptual span adjustment emerged early in development at around second grade and remained stable in later grades. We conclude that the local modulation of the perceptual span indicates a general cognitive process, perhaps an attentional gradient with rapid readjustment.
Prediction and error in early infant speech learning: A speech acquisition model
Jessie S. Nixon & Fabian Tomaschek
Cognition, 2021
In the last two decades, statistical clustering models have emerged as a dominant model of how infants learn the sounds of their language. However, recent empirical and computational evidence suggests that purely statistical clustering methods may not be sufficient to explain speech sound acquisition. To model early development of speech perception, the present study used a two-layer network trained with Rescorla-Wagner learning equations, an implementation of discriminative, error-driven learning.
The model contained no a priori linguistic units, such as phonemes or phonetic features. Instead, expectations about the upcoming acoustic speech signal were learned from the surrounding speech signal, with spectral components extracted from an audio recording of child-directed speech as both inputs and outputs of the model. To evaluate model performance, we simulated infant responses in the high-amplitude sucking paradigm using vowel and fricative pairs and continua. The simulations were able to discriminate vowel and consonant pairs and predicted the infant speech perception data. The model also showed the greatest amount of discrimination in the expected spectral frequencies. These results suggest that discriminative error-driven learning may provide a viable approach to modelling early infant speech sound acquisition.
Of mice and men: Speech sound acquisition as discriminative learning from prediction error, not just statistical tracking
Jessie S. Nixon
Cognition, 2020
Age estimation in foreign-accented speech by non-native speakers of English
Dan Jiao, Vicky Watson, Sidney Gig-Jan Wong, Ksenia Gnevsheva & Jessie S. Nixon
More publications
Background photo by Kamto Wong