TREISMAN AND GELADE of perception.However the immediacy and directness of an impression are no guarantee that it reflects an early stage of information processing in the nervous system.It is logically possible that we become aware only of the final outcome of a complicated sequence of prior operations.“T p- do processing may de what we cons as a theory about perceptual coding it needs more objective support (Treis- man,1979). We have recently proposed a new account of attention which assumes that features come first in perception (Treisman,Sykes,Gelade,1977). In our model,which we call the featur egrati theory of attention features are regis ter ed early,automa n paral across the visual field,while objects are identified separately and only at a later stage,which requires focused attention.We assume that the visual scene is initially coded along a number of separable dimensions,such as color, orientation spatial fr requency,brightness, direction of ent.In order to e these separate representations a d to ensure the cor rect synthesis of features for each object in a complex display,stimulus locations are processed serially with focal attention.Any features which are present in the same central''fixation'of attention are combined to form a single object.Thus focal attention provides the "glue"which integrates the initially separable features into unit ary obje cts Once they have been correctly registered,the compound objects continue to be per- ceived and stored as such.However with memory decay or interterence. the features may disintegrate and "float free''once more,or perhaps recombine to form"'illusory coniunctions(Treisman.1977). We claim that,without focused attention,features cannot be related to each other. This poses a problem in ng phe omenal experie There seems to be no way we can consciously perceive an unattac shape without also giving it a color,size,brightness,and location.Yet unattended areas are not perceived as empty space.The integration theory therefore needs some clarification.Our r claim is that attention is neces sary for the correct on n of cor nctions,although unattended features are also conjo ine prior to conscious perc eption. The top-down processing of unattended features is capable of utilizing past experience and contextual information.Even when attention is directed elsewhere. we are unlikely to see a blue sun in a yellow sky.However,in the absence of focused attention and of cffective constraints on top-down processing. conjunctions of features could be formed on a random basis.These unat- tended co will ris to sory ons and physiol evide for the idea that stimuli are initially analyzed along functionally separa though not necessarily by physically distinct channels (Shepard,1964: Garner,1974;De Valois De Valois,1975).We will use the term "di- mension''to refer to the complete range of variation which is separately98 TREISMAN AND GELADE of perception. However the immediacy and directness of an impression are no guarantee that it reflects an early stage of information processing in the nervous system. It is logically possible that we become aware only of the final outcome of a complicated sequence of prior operations. “Top￾down” processing may describe what we consciously experience; as a theory about perceptual coding it needs more objective support (Treis￾man, 1979). We have recently proposed a new account of attention which assumes that features come first in perception (Treisman, Sykes, & Gelade, 1977). In our model, which we call the feature-integration theory of attention, features are registered early, automatically, and in parallel across the visual field, while objects are identified separately and only at a later stage, which requires focused attention. We assume that the visual scene is initially coded along a number of separable dimensions, such as color, orientation, spatial frequency, brightness, direction of movement. In order to recombine these separate representations and to ensure the cor￾rect synthesis of features for each object in a complex display, stimulus locations are processed serially with focal attention. Any features which are present in the same central “fixation” of attention are combined to form a single object. Thus focal attention provides the “glue” which integrates the initially separable features into unitary objects. Once they have been correctly registered, the compound objects continue to be per￾ceived and stored as such. However with memory decay or interference, the features may disintegrate and “float free” once more, or perhaps recombine to form “illusory conjunctions” (Treisman, 1977). We claim that, without focused attention, features cannot be related to each other. This poses a problem in explaining phenomenal experience. There seems to be no way we can consciously “perceive” an unattached shape without also giving it a color, size, brightness, and location. Yet unattended areas are not perceived as empty space. The integration theory therefore needs some clarification. Our claim is that attention is necessary for the correcl perception of conjunctions, although unattended features are also conjoined prior to conscious perception. The top-down processing of unattended features is capable of utilizing past experience and contextual information. Even when attention is directed elsewhere, we are unlikely to see a blue sun in a yellow sky. However, in the absence of focused attention and of effective constraints on top-down processing, conjunctions of features could be formed on a random basis. These unat￾tended couplings will give rise to “illusory conjunctions.” There is both behavioral and physiological evidence for the idea that stimuli are initially analyzed along functionally separable dimensions, al￾though not necessarily by physically distinct channels (Shepard, 1964; Garner, 1974; De Valois & De Valois, 1975). We will use the term “di￾mension” to refer to the complete range of variation which is separately