Perceptual Coherence : Hearing and Seeing

filter inferred from the background change (this is similar to the strategy
proposed in chapter 7 for asymmetric color matching).
Schulz and Sanocki (2003) have demonstrated that proximal (retinal)
and constancy grouping coexist but have different time courses. In fact,
Rock (1997) proposed that initially there is lower-level literal perception
corresponding to the retinal stimulation. If that is inadequate for some reason,
the literal perception is replaced by what he termed a higher-order
world or constancy mode. Usually, the transition from the literal to the
world mode is irresistible, although the literal mode may bias the worldmode
judgment and although it is still possible to make literal-mode judgments.
To make this concrete, although observers grouped by reflectance in
the experiment described above (Rock et al., 1992), it is very likely that
they would be able to group the columns by luminance if asked.
In the later experiment (Schulz & Sanocki, 2003), the exposure time of
a grid similar to that used by Rock et al. (1992) was varied from 200 to
2,000 ms. At the shortest exposure time, nearly all choices were based on
luminance matching (88%). In contrast, at the longest exposure time nearly
all matches were based on reflectance (83%). Schulz and Sanocki proposed
that retinal matching is performed in the earliest cortical regions (V1 or
V2) and that reflectance matching is carried out in V4.
These sorts of results parallel those discussed in chapter 1 with respect
to the perceived motion of spatial gratings through an aperture. Recall that
the initial percept is roughly toward the average of the motion of the two
gratings (i.e., the additive vector direction), what we would call the proximal
percept. This percept is replaced by a perception that is based on the
intersection of the lines of constraint, what we would call constancy or
world mode. The vector average still biased the intersection of constraint
judgments toward the additive vector direction.
Audition
Auditory and Visual Segmentation 403
The issue of when grouping occurs has not been explicitly discussed with
respect to stream segregation. As described above, the default percept is
one of coherence and that it takes several repetitions before streams arise if
several sounds are recycled continuously (Bregman, 1990). Thus, there is a
shift from proximal to distal perceiving.
It is also likely that the overall context determines segregation. We can
imagine the following experiment. We start with a stationary tone with a
spoken-vowel spectrum of harmonic components and add energy at one
frequency. (A natural vowel would not work because it changes its pitch
and spectral content over time.) If the resulting sound were presented for
a short duration, we would then expect the listener to report a funnysounding
sound. This outcome would be analogous to retinal or proximal