Matthew Chalk PhD

Matthew Chalk


Publications:
2013
  Complexity and specificity of experimentally induced expectations in motion perception
Gekas, N, Chalk, M, Seitz, AR & Seriès, P 2013, 'Complexity and specificity of experimentally induced expectations in motion perception' 22nd Annual Computational Neuroscience Meeting: CNS 2013, Paris, France, 13/07/13 - 18/07/13, pp. 355. DOI: 10.1186/1471-2202-14-S1-P355
General Information
Organisations: Institute for Adaptive and Neural Computation .
Authors: Gekas, Nikos, Chalk, Matthew, Seitz, Aaron R & Seriès, Peggy.
Number of pages: 1
Publication Date: 1 Jan 2013
Publication Information
Category: Poster
Original Language: English
DOIs: 10.1186/1471-2202-14-S1-P355
  Complexity and specificity of experimentally-induced expectations in motion perception
Chalk, M, Seitz, AR, Seriès, P & Gekas, N 2013, 'Complexity and specificity of experimentally-induced expectations in motion perception' Journal of Vision, vol 13, no. 4, 8. DOI: 10.1167/13.4.8
Our perceptions are fundamentally altered by our expectations, i.e., priors about the world. In previous statistical learning experiments (Chalk, Seitz, & Seriès, 2010), we investigated how such priors are formed by presenting subjects with white low contrast moving dots on a blank screen and using a bimodal distribution of motion directions such that two directions were more frequently presented than the others. We found that human observers quickly and automatically developed expectations for the most frequently presented directions of motion. Here, we examine the specificity of these expectations. Can one learn simultaneously to expect different motion directions for dots of different colors? We interleaved moving dot displays of two different colors, either red or green, with different motion direction distributions. When one distribution was bimodal while the other was uniform, we found that subjects learned a single bimodal prior for the two stimuli. On the contrary, when both distributions were similarly structured, we found evidence for the formation of two distinct priors, which significantly influenced the subjects' behavior when no stimulus was presented. Our results can be modeled using a Bayesian framework and discussed in terms of a suboptimality of the statistical learning process under some conditions.
General Information
Organisations: Institute for Adaptive and Neural Computation .
Authors: Chalk, Matthew, Seitz, Aaron R., Seriès, Peggy & Gekas, Nikos.
Publication Date: Mar 2013
Publication Information
Category: Article
Journal: Journal of Vision
Volume: 13
Issue number: 4
Original Language: English
DOIs: 10.1167/13.4.8
  Attention as Reward-Driven Optimization of Sensory Processing
Chalk, M, Murray, I & Seriés, P 2013, 'Attention as Reward-Driven Optimization of Sensory Processing: Neural Computation' Neural Computation, vol 25, no. 11, pp. 2904-2933. DOI: 10.1162/NECO_a_00494
Attention causes diverse changes to visual neuron responses, including alterations in receptive field structure, and firing rates. A common theoretical approach to investigate why sensory neurons behave as they do is based on the efficient coding hypothesis: that sensory processing is optimized toward the statistics of the received input. We extend this approach to account for the influence of task demands, hypothesizing that the brain learns a probabilistic model of both the sensory input and reward received for performing different actions. Attention-dependent changes to neural responses reflect optimization of this internal model to deal with changes in the sensory environment (stimulus statistics) and behavioral demands (reward statistics). We use this framework to construct a simple model of visual processing that is able to replicate a number of attention-dependent changes to the responses of neurons in the midlevel visual cortices. The model is consistent with and provides a normative explanation for recent divisive normalization models of attention (Reynolds & Heeger, 2009).
General Information
Organisations: Neuroinformatics DTC.
Authors: Chalk, Matthew, Murray, Iain & Seriés, Peggy.
Number of pages: 30
Pages: 2904-2933
Publication Date: 18 Jun 2013
Publication Information
Category: Article
Journal: Neural Computation
Volume: 25
Issue number: 11
ISSN: 0899-7667
Original Language: English
DOIs: 10.1162/NECO_a_00494
2010
  Attention Reduces Stimulus-Driven Gamma Frequency Oscillations and Spike Field Coherence in V1
Chalk, M, Herrero, JL, Gieselmann, MA, Delicato, LS, Gotthardt, S & Thiele, A 2010, 'Attention Reduces Stimulus-Driven Gamma Frequency Oscillations and Spike Field Coherence in V1' Neuron, vol 66, no. 1, pp. 114-125. DOI: 10.1016/j.neuron.2010.03.013
Rhythmic activity of neuronal ensembles has been proposed to play an important role in cognitive functions such as attention, perception, and memory. Here we investigate whether rhythmic activity in V1 of the macaque monkey (macaca mulatta) is affected by top-down visual attention. We measured the local field potential (LFP) and V1 spiking activity while monkeys performed an attention-demanding detection task. We show that gamma oscillations were strongly modulated by the stimulus and by attention. Stimuli that engaged inhibitory mechanisms induced the largest gamma LFP oscillations and the largest spike field coherence. Directing attention toward a visual stimulus at the receptive field of the recorded neurons decreased LFP gamma power and gamma spike field coherence. This decrease could reflect an attention-mediated reduction of surround inhibition. Changes in synchrony in V1 would thus be a byproduct of reduced inhibitory drive, rather than a mechanism that directly aids perceptual processing.
General Information
Organisations: Neuroinformatics DTC.
Authors: Chalk, Matthew, Herrero, Jose L., Gieselmann, Mark A., Delicato, Louise S., Gotthardt, Sascha & Thiele, Alexander.
Pages: 114-125
Publication Date: 1 Apr 2010
Publication Information
Category: Article
Journal: Neuron
Volume: 66
Issue number: 1
ISSN: 0896-6273
Original Language: English
DOIs: 10.1016/j.neuron.2010.03.013
  Rapidly learned stimulus expectations alter perception of motion
Chalk, M, Seitz, AR & Series, P 2010, 'Rapidly learned stimulus expectations alter perception of motion' Journal of Vision, vol 10, no. 8, 2. DOI: 10.1167/10.8.2
Expectations broadly influence our experience of the world. However, the process by which they are acquired and then shape our sensory experiences is not well understood. Here, we examined whether expectations of simple stimulus features can be developed implicitly through a fast statistical learning procedure. We found that participants quickly and automatically developed expectations for the most frequently presented directions of motion and that this altered their perception of new motion directions, inducing attractive biases in the perceived direction as well as visual hallucinations in the absence of a stimulus. Further, the biases in motion direction estimation that we observed were well explained by a model that accounted for participants' behavior using a Bayesian strategy, combining a learned prior of the stimulus statistics (the expectation) with their sensory evidence (the actual stimulus) in a probabilistically optimal manner. Our results demonstrate that stimulus expectations are rapidly learned and can powerfully influence perception of simple visual features.
General Information
Organisations: Institute for Adaptive and Neural Computation .
Authors: Chalk, Matthew, Seitz, Aaron R. & Series, Peggy.
Keywords: (expectation, motion perception, Bayesian, attention, psychophysics, , , . )
Number of pages: 18
Publication Date: Jul 2010
Publication Information
Category: Article
Journal: Journal of Vision
Volume: 10
Issue number: 8
ISSN: 1534-7362
Original Language: English
DOIs: 10.1167/10.8.2

Projects:
Visual attention: how does it alter perception, and why? (PhD)