Denis Pelli and Jeremy Freeman
Professor of Psychology and Neural Science, NYU
Graduate Student at Center for Neural Science, NYU
February 15, 2011
Compulsory pooling of crowded objects. A mixture model
Unless we fixate directly on it, it is hard to see an object among other objects. This breakdown in object recognition is called "crowding" and severely limits peripheral vision. The effect is more severe when objects are more similar. When observers mistake the identity of a "target" object among "flanker" objects, they often report a flanker. Many have taken these flanker reports as evidence of internal substitution of the target by a flanker. Here, we ask observers to identify a target presented between one similar and one dissimilar flanker. The supposed substitution process takes in only one of the three letters, which is often the target but, by unwitting mistake, is sometimes a flanker. Having taken only one letter, the substitution process knows only its identity, not its similarity to the target. Thus, the substitution process must report both kinds of flanker - similar and dissimilar - equally often. Contrary to this prediction, we find that the similar flanker is reported much more often than the dissimilar flanker. This refutes the suggestion that rampant flanker substitution accounts for most flanker reports. Mixture modeling shows that substitution can account for at most about half the trials. The rest require pooling, taking information from target and flankers. Thus, pooling, not substitution, is needed to explain the impairment of recognition by other objects.