A Statistical Approach to Visual Masking and Spatial Attention

A stimulus (mask) reduces the visibility of another stimulus (target) when they are presented in close spatio-temporal vicinity of each other, a phenomenon called visual masking. Visual masking has been extensively studied to understand the dynamics of information processing in the visual system. Visual spatial attention is also known to modulate information processing and transfer within the visual system. Since both processes control the transfer of information from sensory memory to visual short-term memory (VSTM), a natural question is whether these processes interact or operate independently. Here, we modeled visual masking by using a statistical framework, and used this theoretical framework along with psychophysical experiments to determine whether and how masking and attention interact. In a psychophysical experiment, observers were asked to report the orientation of a target bar under three different masking paradigms. The distribution of response errors was modeled by using statistical mixture-models. Our results show that in all three types of masking, the reduction of a target’s signal-to-noise ratio (SNR) was the primary process whereby masking occurred. We interpret these findings as the mask reducing the target’s SNR (i) by suppressing or interrupting the signal of the target in para-/meta- contrast, (ii) by increasing noise in pattern masking by noise, and (iii) a combination of the two in pattern masking by structure. Recent evidence suggests that the studies that reported interactions between masking and attention suffered from ceiling and/or floor effects. We investigated interactions between metacontrast masking and attention by using an experimental design in which saturation effects were avoided. In these experiments, attention was controlled either by set-size or by spatial pre-cues. We examined attention-masking interactions based on two types of dependent-variables: (i) the mean absolute response errors and (ii) the distribution of signed response errors. Our results show that both the voluntary (endogenous) and reflexive (exogenous) mechanisms of attention affect observers’ performance without interacting with masking. Statistical modeling of response errors suggests that attention and metacontrast masking exert their effects mainly through independent modulations of the guessing component of the mixture model. Taken together, our results suggest that visual masking and attention operate independently.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Electrical Engineering

Grantor

University of Houston

Year dc:date.issued

2015

Author dc:creator

• Agaoglu, Sevda

Advisor dc:contributor.advisor

• Ogmen, Haluk

Committee members dc:contributor.committeemember

• Breitmeyer, Bruno G.
• Jansen, Ben H.
• Sheth, Bhavin R.
• Zouridakis, George

• Visual masking
• Spatial attention
• Bayesian models
• Metacontrast masking
• Paracontrast masking
• Pattern masking by noise
• Pattern masking by structure

Statement dc:rights

• The author of this work is the copyright owner. UH Libraries and the Texas Digital Library have their permission to store and provide access to this work. UH Libraries has secured permission to reproduce any and all previously published materials contained in the work. Further transmission, reproduction, or presentation of this work is prohibited except with permission of the author(s).

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/10657/3350

OAI identifier oai:identifier

oai:uh-ir.tdl.org:10657/3350