Hierarchical stages in the processing of visual information

Previous research had indicated that when subjects are instructed to report one of a number of visually displayed items, both the number and spacing of the presented material affect report accuracy and latency. The present experiment sought to determine the nature and temporal course of the interference provided by nonattended visual material. Subjects reaction times were measured for deciding which of two targets occupied the indicated position in one or eight element displays. Placing replicas of the target in nonindicated display positions was equivalent to presenting the target alone. Members of the opposite response set produced maximum interference, while encodable and unencodable noise elements not belonging to a response set produced an intermediate decrement. For all display types, presenting the indicator prior to display onset decreased reaction time. Dividing each of the display elements into two parts and presenting the parts asynchronously provided evidence that subjects were indifferent to the presence of complete forms for the first 50 msec. These results were interpreted as supporting the existence of a hiararchical sequence of stages consisting of a preattentive stage which segregates the input into objects and an attentive stage which is likened to a spatial scanner responsible for synthesizing the crude preattentive features into recognized forms. The concurrent operation of these stages provides for the redirection of attention when changes in the input are detected.