Fixed or variable noise in contrast discrimination? The jury's still out


The ability to distinguish one visual stimulus from another slightly different one depends on the variability of their internal representations. In a recent paper on human visual-contrast discrimination, Kontsevich et al (2002 Vision Research 42 1771 - 1784) re-considered the long-standing question whether the internal noise that limits discrimination is fixed (contrast-invariant) or variable (contrast-dependent). They tested discrimination performance for 3 cycles deg-1 gratings over a wide range of incremental contrast levels at three masking contrasts, and showed that a simple model with an expansive response function and response-dependent noise could fit the data very well. Their conclusion - that noise in visual-discrimination tasks increases markedly with contrast - has profound implications for our understanding and modelling of vision. Here, however, we re-analyse their data, and report that a standard gain-control model with a compressive response function and fixed additive noise can also fit the data remarkably well. Thus these experimental data do not allow us to decide between the two models. The question remains open. [Supported by EPSRC grant GR/S74515/01]

Divisions: Life & Health Sciences > Optometry
Life & Health Sciences
Additional Information: Abstract published in Images, Perception, and Psychophysics, Perception, 34 (2), p.246, ISSB 0001-4966.
Event Title: Images, Perception, and Psychophysics. 9th Applied Vision Association Christmas Meeting
Event Type: Other
Event Dates: 2004-12-16
Uncontrolled Keywords: visual stimulus,variability,internal representations,human visual-contrast discrimination,visual-discrimination,compressive response function,fixed additive noise
["eprint_fieldopt_dates_date_type_" not defined] Date: 2005
Authors: Georgeson, Mark A. ( 0000-0002-8173-9522)
Meese, Timothy S. ( 0000-0003-3744-4679)


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