At the Helmholtz Instituut (http://www.phys.uu.nl/~wwwfm/), department
Physics of Man, of Utrecht University (The Netherlands) we have a post doc
position available for a period of two years, starting at the earliest
convenience. The topic is "Visual perception of material properties". The
lab is headed by Jan Koenderink and Astrid Kappers. Interested persons
should contact one of us by e-mail (a.m.l.kappers@phys.uu.nl,
j.j.koenderink@phys.uu.nl).
Short project description:
The human observer effortlessly perceives both the spatial layout of the
environment and the shapes of significant objects. Apart from these
geometrical aspects, the observer perceives the qualities of objects, that
is to say aspects of their chemical constitution, physical properties, and
so forth. For instance, one easily classifies objects as made of wood,
metal, paper or cloth, ... being polished, rough or hairy, ... being dry,
wet or greasy, ... This project aims at the development of novel tools to
probe human perception of material properties.
We start from the assumption that physical descriptions of the stimulus
domain are available. Possible methods are: measurement of discrimination
thresholds in a parameterised continuum of stimuli, direct scaling methods
in which the subject rates stimuli on a subjective scale, indirect scaling
methods in which the subject compares stimuli with respect to a perceptual
attribute and methods of adjustment in which the observer is asked to
adjust parameter values such that a certain perceptual state is achieved.
Methods of adjustment are convenient because they allow one to obtain much
data in a relatively short period and they appear as very "natural" tasks
to the observers: In the case of the perception of material properties the
problem is much the same as that faced by the painter. For instance, how
should one change a coloured area such that it looks "shiny", "wet", or
"metallic"? We are often in a position to predict which "knobs to turn" in
order to arrive at a desired effect.
We have identified various aspects of the proximal stimulus that are likely
candidates as "cues" for the perception of material attributes. These can
be parametrically varied in a controlled manner thus enabling
psychophysics. We plan to work on aspects of texture, BRDF (Bidirectional
Reflection Distribution Function) and surface roughness.
Helmholtz Instituut
Princetonplein 5
3584 CC Utrecht
The Netherlands
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