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Intermodal perception of whether an
object is within reach |
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Behavior causes simultaneous changes in
multiple forms of ambient energy (e.g., light, sound, pressure). The
structure of these changes is specific to the dynamics of the
animal-environment (AE) system, and as such contains information
about the animal relation to the world. Structures exist within
ambient energy arrays (e.g., optical looming sound intensity
increase) but also extend across energy arrays. The patterns
extending across arrays are not contained in individual energies,
exactly as relative optical velocity (e.g. for separation in depth)
is not contained in individual velocity vectors. Though, most
research on multimodal perception consider stimuli available to
individual perceptual systems as independent from each other and
focus on how the relational information could be reconstructed in
the nervous system. An alternative view is to consider the patterns
extending across different forms of stimulation (i.e., patterns in
the global array) as perceptual information available to the animal
(Stoffregen & Bardy, 2001). We evaluated perceptual sensitivity to the global array in the context of egocentric distance perception. The angles and angular motions in optic flow are ambiguous relative to absolute physical distances, and as such do not provide scaled information about ego-distance (e.g., Eriksson, 1973). We formalized an intermodal relation specifying absolute egocentric distance across optical and gravito-inertial flows. In two experiments, we manipulated the availability of this intermodal pattern to evaluate whether and how it influenced humans’ ability to judge verbally whether an object is within reach. |
Target’s display (viewed monocularly)
was driven in real time by the movement of the participant, allowing
us to simulate the virtual target at different distances. As
expected, participants’ reachability judgments were far more precise
and accurate when the intermodal relation between optical and
gravito-inertial flows was preserved, as compared to a control
condition in which participants remained stationary while they were
shown the same optic flow, played back as open-loop stimuli.
Participants’ exploratory movements were concentrated around a
unique axis whose direction was consistent within participants and
movement’s range increased as target’s distance increased. The
differences in judgments’ accuracy appeared related to the use of
specific movement trajectories for which the equations specifying
distance simplify. Preliminary results from another experiment in
which we added an acoustical dimension seem to confirm humans’
sensitivity to the global array. Eriksson, E. S. (1973). Distance perception and the ambiguity of visual stimulation - A theoretical note. Perception and Psychophysics, 13, 379-381 Stoffregen, T.A. & Bardy, B.G. (2001). On specification and the senses. Behavioral and Brain Sciences, 24(2), 195-261. This research was supported by the Enactive Interfaces European Network of Excellence (IST #002114). |
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