Figure

Intact figures (left-hand side), with degraded line drawings either preserving (middle column) or not preserving (far-right column) parts of the contour providing information about concavities. Adapted from Biederman (1987).

they took less time to decide that an orange-coloured asparagus was not a carrot, even though the visually presented colour of the asparagus was the same as that of carrots.

Biederman (1987) argued that the input image is initially organised into its constituent parts or geons, with geons forming the building blocks of object recognition. However, as we saw earlier, global processing of an entire object often precedes more specific processing of its parts (see Kimchi, 1992).

In sum, there is some experimental support for the kind of theory proposed by Biederman (1987). However, the central theoretical assumptions have not been tested directly. For example, there is no convincing evidence that the 36 components or geons proposed by Biederman do actually form the building blocks of object recognition.

Evaluation

As Humphreys and Riddoch (1994) pointed out, many theories of object recognition (e.g., those of Marr and Nishihara, and of Biederman) propose that object recognition depends on a series of processes as follows:

• Grouping or encoding into higher-order features.

• Matching to stored structural knowledge.

• Access to semantic knowledge.

These theories have the great advantage over earlier theories of being more realistic about the complexities of recognising three-dimensional objects. However, they are still rather limited. First, these theories are reasonably effective when applied to objects having readily identifiable constituent parts, but they are much less so when applied to objects that do not (e.g., clouds).

Second, Biederman (1987) argued that edge-based extraction processes provide enough information to permit object recognition. As we have seen, evidence for this hypothesis was reported by Biederman and Ju (1988), who found that object recognition was as good with line drawings as with colour photographs. However, Sanocki et al. (1998) pointed out that such evidence only supports the hypothesis provided that line drawings consist only of edges that are present in the original stimulus. In fact, line drawings are

Object recognition as a function of stimulus type (edge drawings vs. colour photographs) and presence vs. absence of context. Data from Sanocki et al. (1998).

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