The so-called changed-blindness phenomena has given some clues of how human vision and perception really works and it is, therefore, interesting to examine the results of the related studies and to make conclusions upon this. Precisely this will be the effort of this brief paper which will deal with the contribution changed blindness studies have made to the understanding of vision and perception (Levin et al, 2000; Shapiro, 2000; Simons, 2000).
Recent psychological investigations have revealed that almost nobody is very good at remarking supposedly obvious changes to visible elements of the environment. For example, it has been discovered that most individuals miss out to detect significant changes to scenes while watching a movie. The detection failures are remarkable and include the viewer even not detecting when a conversation partner has being exchanged with another (e.g. Grimes, 1996; Blackmore et al, 1995; Pashler, 1988; Phillips, 1974; Levin & Simons, 1997; cited in Simons 2000). As proposed by Noe et al (2000) these kinds of change-blindness studies can be divided into three central categories (see Intraub, 1997; Simons & Levin, 1997):
A) The first experiments mainly aims at illustrating how changes occurring during saccades have a crucial effect on individuals being able to perceive changes in natural landscape photographs (Grimes, 1996). This category of change-blindness studies was preceded by experiments on the blending of visual information across saccadic eye movement (McConkie and Zola, 1979).
B) The second category of change-blindness studies provides support for the notion that detection failure of changes is unrelated to saccade-dependent mechanisms of suppression (Rensink et al, 1997).
In other words, experiments create so-called flicker conditions for participants and test their ability to detect changes in images under these modified conditions. The findings suggest that individuals even fail to detect usually observable changes in flicker conditions where a blank mask appears after the display of every image. Additionally change detection failures are also found to be significantly influenced by mud splashes which appeared at the same time as the changes in experiments but never at the same places as the changes (O’Regan et al., 1996). Conclusively, eye blinks have the same effect on detecting changes and reduce the capability to successfully detect alterations on static or moving images (O’Regan, et al, 1997). Rensik et al (1997) have maintained that these discoveries can be understood in terms of that attention uses motion transients only as low-level cues for direction and that the visual perception of change in a scene occurs only when focused attention is given to the part being changed (p. 368).
C) A third group of studies emphasises the fact that the change-blindness phenomenon is not only restricted to experimental laboratory conditions but also evident in real life settings. Experiments revealed that individuals do even rarely recognise when their conversation partner is exchanged while they are concentrating on a high demanding task (Simons and Levin, 1998; cited in NoA« et al, 2000).
In sum, all three categories of change blindness studies imply, according to NoA« et al (2000), that individuals only spot alterations to elements that the visual system has encoded. Consequently, when people normally view objects or persons the major part of the environment is left decoded. However, it still remains unanswered by scientists what factors determine the encoding of certain features of the environment and why are particular details left decoded and not other details, although, it has been asserted (e.g. Rensink et al., 1997) that attention is pivotal in the decision making of the visual system. Rensink et al (1997) came to this conclusion as it was demonstrated through the modification of the exposure duration that neither memory processing nor perceptual limitations do account for this phenomenon. This view was supported by Simons and Levin (1997) who ascertained that although the memory can capture the draft of an image to a high degree it cannot manage to retain more detailed and explicit items of an image. Additionally change-blindness experiments helped, additionally, to back up the assumption that aspects of images which are in the focus of interest and in the centre of attention suffer less from change detection failures.
This fact led Simons and Levin again to conclude that more specific details really need to be encoded into the working memory before being able to use them for comparisons with upcoming images or frames and that this processing is mainly done with items which are in the centre of attention. The discovery that attention is a key player for visual details of images being thoroughly captured by the viewer is not a new finding but was also established in so-called AB (attentional blink experiments) (see Shapiro et al, 1994; Simons, 2000b; Simons and Levin, 1998) where two stimuli are rapidly and consequently shown to the participant and where the participant has to detect both as fast as possible and correctly. AB studies have demonstrated that if the participants’ attention was laid on the first stimulus there were more mistakes made in the correct and timely detection of the second stimulus. One comes to the same conclusion as with the change-blindness phenomena that detection failures of the visual system arise when insufficient and inappropriate attention is available (Shapiro, 2000).
Reconstructionist have used the change-blindness phenomena to support their conception of vision which includes the notion of the whole world being an illusion itself (grand illusion theory) They claim that if visual processes are merely represented through neural processes, and if retinal information is used to build detailed internal models of an image, the fact that not vision is responsible for the construction of such detailed models proofs that the detail is in truth not seen but solely cognitively constructed. However this theory was vehemently rejected by most scientists researching in this area (e.g. NoA« et al, 2000; Shapiro, 2000).
As a matter of fact, there are nowadays many other investigated phenomena like, for instance, visual stability despite eye movement or filling-in which have, in addition to change-blindness experiments, established the notion neural bases of vision may not require elaborate world-model construction and that visual science should reject the traditional reconstructionist conception of vision (NoA« et al, 2000, p. 104).
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