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Biology 202
2003 Second Web Paper
On Serendip

Change Blindness

Erin Fulchiero

After investigating spatial cognition and the construction of cognitive maps in my previous paper, "Where Am I Going? Where Have I Been: Spatial Cognition and Navigation", and growing in my comprehension of the more complex elements of the nervous system, the development of an informed discussion of human perception has become possible. The formation of cognitive maps, which serve as internal representations of the world, are dependent upon the human capacities for vision and visual perception (1). The objects introduced into the field of vision are translated into electrical messages, which activate the neurons of the retina. The resultant retinal message is organized into several forms of sensation and is transmitted to the brain so that neural representations of given surroundings may be recorded as memory (2). I suggested in my previous paper that these neural representations must be maintained and progressively updated with each successive change in environment and movement of the eye. Furthermore, I claimed that this information processing produces a constant, stable experience of a dynamic, external world (1). However, myriad studies and the testimony of any motorist who has had the unfortunate experience of hitting an unseen object, contradict the universality of that claim and illuminate a startling reality: human beings do not always see those objects presented in their visual field nor alterations in an observed scene (3,4,5,6,7,8,9). The failure to consciously witness change when distracted for mere milliseconds by saccade or artificial blink events is referred to as "change blindness." In order to comprehend this phenomenon, the physical act of looking and the process of seeing must be differentiated. Through an examination of change blindness, we may confirm and attempt to explain this distinction.

The concept of change blindness has been addressed over the course of nearly half a century, with increasing focus on the subject throughout the past five years (3). Although biologists, psychologists, and philosophers have yet to resolve definitively the paradox of looking without seeing, the investigation of each theory on the matter yields deeper insight into visual perception and sight as well as a decreasingly incorrect understanding of those components of the nervous system, which are crucial for visual cognition. Under normal viewing conditions, changes produce transient signals that can draw attention. Change blindness studies are designed to eliminate or block these transient signals by inserting a visual disruption when the change occurs (3). Flicker Paradigm studies examine the occurrence of change blindness and attempt to explain the inability to not see that which is directly in front of our eyes. The Flicker Paradigm demonstrates the essentiality of attention in the process of seeing (4). The alternation of an object and a modified version of that same object is interrupted by millisecond flashes of blank space. Subjects are then asked to report changes in the images.

In order understand the events leading to the failure to recognize change, comprehension of the mechanism by which change is successfully recognized is requisite. According to the traditional understanding of this process, an individual must form an internal representation of the initial display. Then, comparison must be made between the first and second display. Because the initial display is no longer available, the internal representation must be retained for comparison to the second display. Finally, conscious access to the results of this comparison must be available. To explicitly report the change, the observer must be acutely aware of those results. Change blindness, then, is a product of failure in at least one of these three component processes (5). Although the majority of theories on change blindness focus on failed creation of representation or comparison, failed detection has been shown to occur even in the presence of accurate formation of a representation if a proper comparison is not made between that representation and the second display (6). Furthermore, a comparison does not guarantee the avoidance of change blindness if any fault exists with the representation including insufficient detail or entire absence of the changed feature (7).

This same mechanism involved in the perception of change has been investigated through the Flicker Paradigm and described in terms of memory. According to this paradigm, change perception is a highly integrated process involving several steps. First, information must be loaded into visual short-term memory (VSTM) (3). A subject must retain that information over the duration of the blank interval, compare the stored to the visible information in the new display and unload the VSTM and shift attention to a new location. Without focused attention, representations of objects within the brain are ephemeral and no conscious detection of change can occur. Focused attention, therefore, acts as the mediator of change perception by giving objects coherence across time and space (8). Interestingly, much proof exists that something even beyond anticipation of a change must be present for the observation of change. Rensink has shown that even when instructed to look for change, a task that leads subjects to actively attend an image, change can go undetected (4).

The theoretical explanations for the malfunction of change perception are dependent upon the two common understandings of this capacity. The first of these theoretical approaches begin with the assumption that the creation of internal representations of the outside world and subsequent activation of those representations allow us to engage in the experience of seeing. The other prominent approach suggests instead that the world functions as its own external representation, and sight is enabled once an organism has mastered the governing laws of sensorimotor contingency (9). Those who subscribe to the notion of the creation of an internal representation of surroundings attribute change blindness to the sparseness of this representation (4). Thus, only those environmental objects encoded as interesting are attended and seen. When a distracting factors draws attention away from an object observed without attention, a change in that object goes unnoticed because it was not properly and initially represented in the internal image (3). The proponents of the second philosophy, however, contend that the structure of the rules that govern visual perception, sensorimotor contingencies, and the knowledge of those rules mediate the explorative activity which visual perception is understood to be ( 9). A distinguishing law or contingency is the fact that when the eyes close during blinks, the stimulation changes drastically, becoming uniform: the retinal image goes blank. Scientists holding these beliefs suggest that vision requires the satisfaction of two basic conditions. First, the environment must be explored in a manner governed by sensorimotor contingencies, both fixed by the visual apparatus, and those fixed by the character of the observed objects. Second, the brain of the observer must be actively exercising mastery of the laws of sensorimotor contingencies. These theories question the formation of an internal representation under the flicker paradigm circumstances, suggesting instead that the external environment serves as its own representation for immediate probing during which change blindness can occur (9). Results of experiments conducted on these bases show the very presence of a visual stimulus may obligatorily cause observers to make use of the world in the "outside memory" mode, even though it is less efficient that normal memory processing.

In both theoretical approaches, findings suggest limitations on the amount of information that can be consciously retained and compared between two views, even over short delays (6). Thus, successful change detection requires attention to be focused on an object. And yet, all details and aspects of even those objects under close attendance are often only partially retained and compared across views. Visual perception is an extraordinarily complex function, immense in the levels of processing as well as in its differential success in variable tasks. This variation in capability results from the components of perception and their respective operations. For example, short-term visual memory, which essential for detection of change, is found to exhibit exquisite performance in memory tasks but has a decreased threshold under certain circumstances (6). Current research is valuable, not for its conclusive findings regarding the occurrence of change blindness, but for the implications it holds for perception and for the future of its study. Work is being done continuously to elucidate the relative roles of spatial location, memory, sensory and attentional mechanisms, and general psychophysical capacities in response to specific cognitive demands (3, 7, 9, 10). By exemplifying the potential for failure of a system that we assume to work flawlessly in our daily interactions, change blindness has incited uniquely directed investigations of visual consciousness and facilitated the overall comprehension of the human neurological experience.


1)"Where Am I Going? Where I Have Been", First Web Paper

2)Human Position Sense and Spatial Maps, a resource on spatial cognition

3)Rensink Collection, a grouping of articles by one of the creators of the Flicker Paradigm

4) Annual Review of Psychology , an article by Ronald Rensink on change detection and visual perception

5)Cognet, a site on Cognition

6)Memory For centrally attended changing objects in an incidental real world change, An article by Levin, Simons, Angelone, and Chabris

7) Scott-Brown, K.C. & Orbach, H.S. (1998) "Contrast Discrimination, Non-Uniform Patterns and Change Blindness". Proceedings of the Royal Society of London. 256 (1410): 2159-2164.

8)Max Planck Institute

9)A sensorimotor account of vision and visual consciousness , Behavioral and Brain Sciences article from 2001

10)Glasgow Caledonian University, current research in vision sciences

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