The preceding experiments show that under flicker conditions, observers can take a surprisingly long time to perceive large changes in images of real-world scenes. This difficulty is due neither to a disruption of the information received nor to a disruption of its storage. It does, however, depend greatly on the significance of the part of tbe scene being changed, with identification being faster for structures of central interest than for those of marginal interest. We therefore make the following proposal: • Visual perception of change in an object occurs only when that object is given focused attention; • In the absence of focused attention, the contents of visual memory are simply overwritten (i.e., replaced) by subsequent stimuli, and so cannot be used to make comparisons. Although it is not yet possible to specify the detailed operation of the atlentional mechanisms involved, it is likely that the allocation of attention causes the relevant structures to form object files (Kahneman. Treisman, & Gibbs, 1992), or at least lets them be entered into a relatively durable store, such as visual short-term memory (e,g., Coltheart, 1980; Irwin, 1991; Sperling, 1960), so that comparisons can be made. In this view, all the effects encountered in these experiments can be traced back to the allocation of attention, which is either “pulled” by transient motions or “pushed” by volitional control (e.g., Kleiti et al., 1992; Posner, 1980). Under normal conditions, the motion signals resulting from a change draw attention to its location and so allow the observer to perceive it. When these signals are delocalized by flicker, their influence is effectively removed; attention is then directed entirely by static low-level properties such as feature gradients (Nothdurft, 1992) and high-level volition. If there are no distinct low- or high-level cues (true of most stimuli we used), detection of change will require a slow, item-by-item scan of the entire image, giving rise to long identification times. The faster identification of CI than MI changes—despite the smaller area of the Cl changes—would result from the attraction of attention via the high-level interest of CI objects.
Nursingmodules.com is a custom nursing writing service that provides online custom-written papers, such as term papers, research papers, thesis papers, essays, dissertations, and other custom writing services inclusive of research materials for assistance purposes ONLY. Proper reference should be used
4870 Cass Ave
Detroit, MI, United States
+1 (628) 261-0844