Extent and profile of the attentional field revealed with the use of luminance gradients in the motion induction effect

Academic Article

Abstract

  • Purpose. The involvement of an attentional speed-up of processing in causing the illusory motion in a bar presented next to and following the presentation of a priming spot (motion induction, MI), and the ability of a luminance gradient within the bar to cancel the priming effect have been shown previously (von Grünau et al., ARVO 1995, S372). Here we used this technique to measure the extent and profile of the attentional field around the priming spot. Methods. In a MI paradigm with a primer at each end of the bar (split priming), we determined the luminance gradient necessary to just cancel the illusory motion away from the second primer produced by a sufficiently long delay of the second with respect to the first primer. A 2AFC method was used. Independently the detection RT for spots of different luminance was measured. These experiments were done for bars varying in length between 1.1 and 7.4 degrees, and for linear and quasi-exponential gradients. Results. The processing time difference between the two bar ends (processing speed-up, size of MI) first increased and then decreased with bar length. The exact relationships varied largely between individuals. From the time differences, we calculated the speed of the illusory motion (which increased with increasing bar length) and the profile of the attentional field. The diameter of the facilitating center varied between 2.1 and 10.6 degrees for different observers. The extent of the inhibiting surround was larger than the bars used here. The type of luminance gradient did not influence the results. Conclusions. These experiments provide further details regarding the attentional field that is present in the vicinity of a suddenly presented spot. It consists of facilitating and inhibiting parts. Cancelling the MI effect with appropriate luminance gradients provides a useful method of studying attentional effects.
  • Authors

    Pubmed Id

  • 18421085
  • Author List

  • Von Grünau MW; Racette L; Iordanova M; Kwas M
  • Volume

  • 37
  • Issue

  • 3