Object-based visual selective attention and perceptual organization

We report the results of four experiments that were conducted to examine bo th the representations that provide candidate entities available for object -based attentional selection and the influence of bottom-up factors (i.e., geometric and surface characteristics of objects) and top-down factors (i.e ,, context and expectancies) on the selection process. Subjects performed t he same task in each of the experiments. They were asked to determine wheth er two target properties, a bent end and an open end of a wrench, appeared in a brief display of two wrenches. In each experiment, Me target propertie s could occur on a single wrench or one property could occur on each of two wrenches. The question of central interest was whether a same-object effec t (faster and/or more accurate performance when the target properties appea red on one vs. two wrenches) would be observed in different, experimental c onditions. Several interesting results were obtained. First, depending on t he geometric (i.e., concave discontinuities on object contours) and surface characteristics (i.e., homogeneous regions of color and texture) of the st imuli, attention was preferentially directed to one of three representation al levels, as indicated by the presence or absence of the same-object effec t. Second, although geometric and surface characteristics defined the candi date objects available for attentional selection, top-down factors were qui te influential in determining which representational level would be selecte d. Third, the results suggest that uniform connectedness plays an important role in defining the entities available for attention selection. These res ults are discussed in terms of the manner in which attention selects object s in the visual environment.