2/15/2006

Mindsight Reconsidered

Prompted by Bob Mottram's justified skepticism of "mindsight", I've found this article (by Dan Simons et al., & also from Psychological Science) which suggests this change blindness phenomenon might be merely a change of response criterion.

"Provocative claims merit rigorous scrutiny," state Simons et al., before they go on to show that mindsight rates are highly correlated with false alarm rates in their replication of Rensink's original study (with a greater number of trials, including catch trials). This is precisely what one would predict if "sensing" is actually a liberal response strategy, and "seeing" requires verification of that initial response over several subsequent alternations between pictures.

According to this logic, more liberal individual response criteria for "sensing" should result in both more "sensing" false alarms and longer lags between "sensing" and "seeing." In other words, subjects in the can-sense group should show more sensing false alarms than only-see subjects, which is inconsistent with "mindsight" being the result of a distinct informative process. Indeed, Simons et al. found a difference of more than 10% in false alarm rates between groups; perhaps the lower number of catch trials used by Rensink provided insufficient power to find this crucial difference (which in his experiment was less than a 1% difference between groups).

Rensink had argued against the "liberal response criterion" explanation with with the following logic: if mindsight is only a different criterion, such partial detection should lead to a more immediate "saw" response. In contrast, Rensink argued, the "sense-saw" lag on mindsight trials was similar to response latency on nonmindsight trials, indicating that mindsight did not contribute to change localization. Simons et al. claim that this finding is a result of Rensink's arbitrary 1-second cut-offs between can-sense and only-see groups.

Although it is certainly tempting to deride such an outlandish hypothesis, non-attentional pathways to awareness do seem to exist as demonstrated by several neuropsychological findings. For example, when patients with right parietal damage are asked to draw two houses (pictured at the start of this article), they are unable to draw the left side of each house, and will proclaim that the two images are identical despite the fact that the left side of one house is on fire; this is a classic demonstration of hemispatial neglect. However, when asked to point to the house in which they'd rather live, most hemispatial neglect patients will point to the house that's not on fire. Such cases demonstrate that visual information is able to guide decision-making even if spatially it is nonspecific (similar to mindsight) and even if it is below the threshold of verbal awareness (similar to blindsight).

In a wonderful example of academic "adversarial collaboration," Rensink and Simons have since co-authored a review of change blindness research which reflects their continuing disagreement about whether mindsight might reflect a new perceptual mechanism, a non-attentional pathway to awareness (such as that demonstrated by hemispatial neglect patients, or those with optic ataxia), or merely the use of multiple response criteria.

Related Posts:
A New Mode of Perception?

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