Evaluation

The Gestalt approach led to the discovery of several important aspects of perceptual organisation. As Rock and Palmer (1990, p. 50) pointed out, "the laws of grouping have withstood the test of time. In fact, not one of them has been refuted, and no new ones have been added." However, they suggested two new laws of grouping themselves:

1. The law of common region, according to which observers tend to group together elements that are contained within the same perceived region or area.

2. The law of connectedness, according to which there is a tendency "to perceive any uniform, connected region—such as a spot, line or more extended area—as a single unit (Rock & Palmer, 1990, p. 50).

The Gestaltists relied heavily on introspective reports, or the "look at the figure and see for yourself' method. More convincing evidence was provided by Pomerantz and Garner (1973). Their participants were presented with stimuli consisting of two brackets arranged in various ways. The task was to sort the stimuli into two piles as fast as possible depending on whether the left-hand bracket was "(" or ")". The participants were instructed to ignore the right-hand bracket, but found it impossible to do this when the two brackets were groupable (e.g., because both brackets were similar in orientation or were close to each other). As a result, there were slower sorting times for groupable stimuli than for non-groupable ones.

The Gestaltists produced descriptions of interesting perceptual phenomena, but failed to provide adequate explanations. They assumed that observers use the various laws of perceptual grouping without the need for relevant perceptual learning, but did not provide any supporting evidence.

The Gestaltists argued that grouping of perceptual elements occurs early in visual processing. This assumption was tested by Rock and Palmer (1990). They presented luminous beads on parallel strings in the dark. The beads were closer to each other in the vertical direction than the horizontal one. As the law of proximity predicts, the beads were perceived as forming columns. When the display was tilted backwards, the beads were closer to each other horizontally than vertically in the two-dimensional retinal image, but remained closer to each vertically in three-dimensional space. What did the observers report? They saw the beads organised in vertical columns. As Rock and Palmer (1990, p. 51) concluded, "Grouping was based on perceived proximity in three-dimensional space rather than on actual proximity on the retina. Grouping by proximity must therefore occur after depth perception." Thus, grouping happens later in processing than was assumed by the Gestaltists.

According to the Gestaltists, the various laws of grouping operate in a bottom-up way to produce perceptual organisation. According to this position, information about the object or objects in the visual field is not used to determine how the visual field is segmented. Contrary evidence was reported by Vecera and Farah (1997). They presented two overlapping transparent letters (see Figure 2.3). The participants' task was to decide as rapidly as possible whether two xs in the figure were on the same shape. The key manipulation was whether the letters were presented in the upright position or upside down.

Vecera and Farah found that performance was significantly faster with upright letters than with upside down ones. This occurred because the two shapes to be segmented were much more familiar in the upright condition. Thus, as Vecera and Farah (1997, p. 1293) concluded, "top-down activation can partly guide the segmentation process." These findings suggest that the Gestaltists may have exaggerated the role of bottom-up processes in segmentation.

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