December 17, 2006

The impact of invisible stimuli


The more clear a stimulus is, the more distracting it can be. Or so you might think. In a recent Science publiation Tsushima et al. report that weak stimuli that are irrelevant to the task being performed—have
a greater impact than strong, easily noticeable distractors.From Science:

The authors used a rapid visual presentation task in which healthy participants had to detect two digits that appeared very briefly in a central stream of six letters. This stream of alphanumeric symbols was surrounded by an annulus of randomly moving dots. Different proportions of these dots — 0 to 20% — moved coherently in the same direction (the “signal”) during the trials. The larger the proportion of these coherently moving dots (the larger the motion coherence ratio of the task-irrelevant background), the more motion one perceives.

Here is the abstract:

Tsushima Y, Sasaki Y, Watanabe T
Science. 2006 Dec 15; 314(5806): 1786-8

Considerable evidence indicates that a stimulus that is subthreshold, and thus consciously invisible, influences brain activity and behavioral performance. However, it is not clear how subthreshold stimuli are processed in the brain. We found that a task-irrelevant subthreshold coherent motion led to a stronger disturbance in task performance than did suprathreshold motion. With the subthreshold motion, activity in the visual cortex measured by functional magnetic resonance imaging was higher, but activity in the lateral prefrontal cortex was lower, than with suprathreshold motion. These results suggest that subthreshold irrelevant signals are not subject to effective inhibitory control.

1 Comment »

  1. As long as a stimulus lies in the visual field it will definitely be registered, processed and normally dealt with in the brain whether consciously or unconsciously seen. More details of my point of view will be included in what I intend to call “RRR” theory to be laid out at one of the coming conferences on consciousness,in the event my abstract is deemed acceptable.

    Comment by Abdu "The One" — March 10, 2007 @ 8:23 am

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