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Developing biologically plausible models of eye movement control and visual processing in reading

Primary Supervisor: Dr David Souto, University of Leicester

Secondary supervisors: Professor Kevin Paterson, Professor Huiyu Zhou

PhD project title: Developing biologically plausible models of eye movement control and visual processing in reading

University of Registration: University of Leicester

Project outline:

The brain’s ability to visually process the tiny squiggles that form letters and words is one of the greatest achievements of mankind. Research on the visual system over the past 50 years has taught us a great deal about visual and cognitive processes involved in reading. The relatively recent use of eye-tracking has accelerated understanding of how the eyes control the influx of complex visual information that we continuously process while reading [1]. This has highlighted how reading depends on making a series of brief fixational pauses, separated by rapid, ballistic movements of the eyes, to obtain a sequence of visual samples (i.e. snapshots of information). However, one aspect that has been largely overlooked, but is potentially important to our ability to read proficiently, is the visual system’s ability to establish correspondences across the visual samples obtained on each fixational pause [2].

When successive words are fixated, a mechanism is required to compute the spatial location of the currently fixated word relative to the previously fixated word. Without such a mechanism, crucial information provided by word order (i.e. that “man bites dog” means something different from “dog bites man”) might be lost. There are several possible correspondence mechanisms that might enable the visual system to keep track of this information (e.g., based on a noisy efference copy signal or attenuated motion signals). The central aim of the current project is to establish how this is achieved and to understand the conditions in which visual instability (i.e. a failure to keep track of the relative spatial location of words) might impact reading.

A first objective is to build a computational model that can simulate biological mechanisms that might keep track of this information. This will involve using computational modelling techniques, combined with experiments using eye-tracking to test how visual information is integrated across eye movements under different correspondence mechanisms, building on existing models of eye movement control [3].

A second objective is to test how reading is impacted by correspondence failure, which in turn will allow us to test the validity of the model. To explore these conditions, we will induce visual instability using gaze-contingent paradigms (e.g. introducing surreptitious shifts in the location of text during eye movements) and measure how the resulting instability impacts on eye dynamics (e.g. duration of the next fixation, probability of a corrective eye movement).

Potential correspondence mechanisms are likely to be vulnerable to age-related cognitive decline [4]. Accordingly, a third objective is to examine age differences in effects of visual instability, by comparing the performance of young and older adults in gaze-contingent paradigms. In sum, the work will advance understanding of biological mechanisms of visual correspondence, and uncover how limitations in their functionality, including due to cognitive ageing, might affect reading ability.

The project brings together a cross-disciplinary supervisory team and will employ a multi-methods approach combining eye-tracking, psychophysics, and computational modelling. The project will also follow best practice in open science, by pre-registering research plans and publishing data, code and outputs using open access methods.

References:

  1. Reichle, ED (2021). Computational models of reading: A handbook. Oxford University Press.
  2. Souto D, Gegenfurtner KR, Schütz AC (2016). Saccade adaptation and visual uncertainty. Hum. Neurosci. 10:227. doi.org/10.3389/fnhum.2016.00227
  3. Engbert R, Longtin A, Kliegl R. (2002). A dynamical model of saccade generation in reading based on spatially distributed lexical processing. Vision Res. 42, 621-636. doi.org/10.1016/S0042-6989(01)00301-7
  4. Brockmole JR, Logie RH (2013). Age-related change in visual working memory: a study of 55,753 participants aged 8–75. Psychology 4:12. doi:10.3389/fpsyg.2013.00012

BBSRC Strategic Research Priority: Understanding the Rules of Life: Neuroscience and behaviour & Integrated Understanding of Health: Ageing

Techniques that will be undertaken during the project:

  • Experimental design
  • Experiment programming using Matlab and Python, data acquisition and data analysis using high-precision eye-tracking
  • Computational modelling of visual and language processing
  • Statistical computing using linear mixed-effects models and the R programming environment

Contact: Dr David Souto, University of Leicester