Perceptual Coherence : Hearing and Seeing

The Transition Between Noise and Structure 161
Figure 4.5. Texture segmentation of simple geometric shapes is determined by
orientation, and not by the perceived similarity of the shapes. The Ts are judged to
be more similar to each other than to the L-like corner. The 45° Ts segregate although
Ts and Ls are judged most dissimilar. Adapted from “Textural Segmentation,”
by J. Beck, 1982, in J. Beck (Ed.), Organization and Representation in
Perception (pp. 285-317). Hillsdale, NJ: Erlbaum.
distinction once again, it is still stuff. Large changes in the positions of
adjacent features are not noticed. To convert stuff to things requires focal
attention. The focal attention binds dots and lines into the micropatterns and
the micropatterns into figural regions. Local features segment textures, not
global-order statistics
In moving away from a statistical to a geometrical explanation, this
work converged on parallel research done by Beck (1982) that started from
a classical Gestalt perspective. Beck began with the working hypothesis
that the similarity between distinct geometric shapes determins the grouping
into discrete regions. Thus, Beck’s arrays were composed of shapes like
lines, angles, Ts, and crosses because it was assumed that the differences in
the local geometrical properties of the shapes determine segmentation
(these shapes are analogous to the later textons of Julesz). In one clear example,
Beck made use of upright Ts, 45° Ts, and upright Ls (figure 4.5).
Based on the concept of effortless grouping, the 45° Ts strongly split off
from the other figures even though the two Ts were judged most similar in
shape; orientation was more important than similarity. What is common to
the work of both Julesz and Beck is the conclusion that texture segmentation
is based on simple physically defined properties that do not necessarily
reflect the similarity between the elements.
Nothdurft (1997) showed that segmentation is not based simply on local
first-order densities. Instead, perceptual segmentation occurs when there is a
sufficiently large difference between regions in terms of luminance, texton,