• As the two photos switched back and forth quickly (with the blank screen in between), participants had to detect the change. • The result was that people had a very difficult time seeing the change. o In most cases, it took many alternations of the photos before people finally detected the change. This illustrates the concept of change blindness in that our internal representation of the world is not as rich as we think. We feel that we perceive all of the information in our visual field with high resolution. However, the fact that we fail to detect very large changes across scenes suggests that this feeling may largely be an illusion. • The illusion of a rich and detailed representation of the external world is said to be the grand illusion of perception . • Rensik et al argued that contrary to our subjective experience, we likely process on or two objects in detail at any given moment. • Grand illusion could be the result of a considerable amount of top-down interpretation of very fragmentary visual information. Rensink et al. also included a condition in which they removed the brief temporal interval (blank screen) and presented the photographs back-to-back. They found that in this condition the change is often seen immediately. • The change is easily detectable in this case because removing the temporal interval leads the changing object to create a flicker, or a motion signal, that draws attention. o The same mechanism is likely operating in the real world. Important changes that might occur while we are driving, for example crease motion signals that draw our attention so we become aware of them. In a study by Simons and Levin (1998), a study confederate would stop passers-by on a college campus to ask them for directions, only to be replaced suddenly by a different confederate when a visual obstacle (two men carrying a large board) passed between them. While the two confederates presented looked different, a large number of people faced with this change failed to detect it. • Change blindness has now been shown to occur with a wide variety of visual disruptions (e.g., blinks, transient noise flashed on a display, etc.). Feature Integration Theory
Chapter 3: Perception The Grand Illusion 20:58 Feature Integration Theory proposed by Anne Treisman suggest that when we initially view objects in our field of vision, we first extract and represent their features (e.g., colour, orientation) across the entire visual field through a process called pre-attentive processing . • As with change blindness, FIT assumes that for an object to be perceived as a whole, there has to be feature binding (the combining of visual features by attention to form whole objects) at a specific location. • Feature binding is accompanied by a stage of processing known as attentive processing , which operates on only a few items at a time in a serial manner.
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- Winter '08