September 2011
Volume 11, Issue 11
Free
Vision Sciences Society Annual Meeting Abstract  |   September 2011
Psychophysical evidence for a common metric underlying number and density discrimination
Author Affiliations
  • Marc Tibber
    UCL, Institute of Ophthalmology, University College London, London, UK
  • John Greenwood
    UCL, Institute of Ophthalmology, University College London, London, UK
  • Steven Dakin
    UCL, Institute of Ophthalmology, University College London, London, UK
Journal of Vision September 2011, Vol.11, 1205. doi:10.1167/11.11.1205
  • Views
  • Share
  • Tools
    • Alerts
      ×
      This feature is available to authenticated users only.
      Sign In or Create an Account ×
    • Get Citation

      Marc Tibber, John Greenwood, Steven Dakin; Psychophysical evidence for a common metric underlying number and density discrimination. Journal of Vision 2011;11(11):1205. doi: 10.1167/11.11.1205.

      Download citation file:


      © ARVO (1962-2015); The Authors (2016-present)

      ×
  • Supplements
Abstract

While observers are adept at judging the density of features present in a visual texture it has recently been proposed that they also have an independent sense of visual number. Here we explore the notion that these abilities tap into a common mechanism. To this end we examined the effects of manipulating the size, contrast and contrast-polarity of individual elements as well as the attentional resources available to the observer. Our prediction is that if a common mechanism underlies density and number judgements then similar effects should be found on discrimination of density and number. Observers (n = 5) always made a 2-IFC discrimination based on the relative numerosity/density of two patches (presented either side of fixation) containing 16–1024 Gaussian blobs. By mismatching patch-size between the two intervals observers were forced to make their judgements based either on density or number. We report that larger stimulus-patches biased perception towards greater density and numerosity, an effect that was amplified under conditions of increased uncertainty about element-size. Mismatching element-size between patches led to large observer biases and elevated thresholds for both density and number discriminations, whilst performance was relatively unaffected by manipulations of element contrast or polarity. Finally, under conditions of increasing attentional load thresholds were similarly elevated for both number and density tasks. Thus, all experimental manipulations had near-identical effects on density and number judgements, supporting the notion of a common underlying metric. Many of our results – in particular the devastating effect of manipulating element-size - are consistent with our model of number/density estimation based not on a representation of individual “objects” but simply on the relative responses of high and low spatial frequency filters.

Funded by the Wellcome Trust. 
×
×

This PDF is available to Subscribers Only

Sign in or purchase a subscription to access this content. ×

You must be signed into an individual account to use this feature.

×