Visual Attention and the Perception of Features and Objects

Feature integration theory (Treisman & Gelade, 1980) suggested that simple features are codel in parallel in a number of specialized feature maps, but that focussed attention is required to ensure the correct integration of features to specify objects. This is done by a serial scan through a master - map of locations, giving access to the features currently occupying the attended location. These are then integrated to form a representation of the object in the selected location. The present paper reviewed new evidence that has accrued since 1980 and elaborated the model to accommodate the recent findings. The proposal is that four different mechanisms may be involved in different conditions: selection of locations, directed by an externally controlled window of attention; selection by features through preattentive grouping; selection of objects; and selection for access to responses.1. The nature of perceptual features has been clarified by experiments suggesting (a) "coarse coding" within dimensions, with just a few values specified for colour, for orientation and for other dimensions, (b) a hierarchical ordering of surface - defining media, each supporting a similar coding of features of shape; (c) separate representations for figures defined by darker and by lighter contrast, with focussed attention required to combine across representations; (d) the idea that feature coding remains parallel and global up to the level that defines surfaces in a three (or perhaps 2 1\2) dimensional world; (e) and finally a distinction between preattention (inaccessible to awareness and to the control of behaviour), inattention (that reflects whatever results of preattentive processing can still be retrieved once attention is redirected), and divided attention (that integrates the preattentive, feature - defined boundaries and allows conscious access to global properties of the display).2. The coding of locations and conjunctions of features has also been further explored. In order to explain fast or parallel search for conjunction targets without any direct coding of conjunctions as such, I and others (e.g., Nakayama & Silverman, 1986; Wolfe et al., 1989; Treisman, 1990) have proposed a second form of attentional selection, controlled not by an externally directed window of attention but by inhibition from one or more separable feature maps. This allows selection of a subset of elements that are spatially intermingled with others rather than grouped in a single spatial window. It also mediates figure - ground segregation on the basis of simple feature differences. The new model differs from my earlier ones in showing parallel access to the shared location map and to the feature maps, making it consistent with the notion of separate parallel pathways coding "what" and "where" (Ungerleider & Mishkin, 1982). When we are given location information in advance (e.g., a spatial cue to where the target will appear), we use the attention window to restrict which features we select. When we have advance information about the relevant features, we use inhibitory control from the appropriate feature maps. When we have neither, we choose an appropriate scale for the attention window and scan serially through locations. …