September 2005
Volume 5, Issue 8
Free
Vision Sciences Society Annual Meeting Abstract  |   September 2005
If we saw it, it must have been where we were looking!
Author Affiliations
  • Eli Brenner
    Neuroscience, ErasmusMC, Rotterdam, The Netherlands
  • Pascal Mamassian
    CNRS, Université Paris 5, France
  • Jeroen B. J. Smeets
    Neuroscience, ErasmusMC, Rotterdam, The Netherlands
Journal of Vision September 2005, Vol.5, 203. doi:10.1167/5.8.203
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      Eli Brenner, Pascal Mamassian, Jeroen B. J. Smeets; If we saw it, it must have been where we were looking!. Journal of Vision 2005;5(8):203. doi: 10.1167/5.8.203.

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

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Abstract

When there is a high degree of uncertainty about a target's position, for instance because the target is moving fast or because it is only visible near the time that the observer makes a saccade, judgments of the target's position are not only unreliable, but they often also contain systematic errors. It is often evident that the systematic errors mainly have a temporal origin. However, there may also be spatial biases. We examined one particular kind of spatial bias: a bias towards the fovea. There is a higher probability of seeing something if it is centred on the fovea than if it is more eccentric. Thus there is also an increased probability that things that one sees are where one is looking. To examine whether uncertainty incites people to localise things closer to the fovea than they really are, we asked subjects to fixate the centre of a screen. A green dot jumped to a new position on this screen every 250 ms (retinal eccentricities between 0.8 and 3.8 deg). At some moment there was a short (one frame) red flash at the screen centre. The subjects' task was to indicate where the green dot had been at the moment of the flash. We analysed subjects' responses in relation to when the flash appeared relative to the sequence of dots. There appeared to be a “delay” (relative to the flash) in selecting a target of about 58ms, with a standard deviation of about 160ms. The temporal bias and temporal uncertainty were independent of the target's eccentricity, but there was a clear tendency to select targets that were close to the fovea. Once a target had been selected, there was a tendency to underestimate its eccentricity if the eccentricity was large, but to overestimate the eccentricity if it was small. This bias can be related to the range of eccentricities encountered during the experiment, but the bias to select less eccentric targets cannot, so the latter is presumably caused by the differences in the probability of seeing things at different eccentricities.

Brenner, E. Mamassian, P. Smeets, J. B. J. (2005). If we saw it, it must have been where we were looking! [Abstract]. Journal of Vision, 5(8):203, 203a, http://journalofvision.org/5/8/203/, doi:10.1167/5.8.203. [CrossRef]
Footnotes
 Supported by the European Commission: project HPRN-CT-2002-00226
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