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TZOFFSETFROM:-0500 TZOFFSETTO:-0400 TZNAME:America/New_York EDT END:DAYLIGHT BEGIN:DAYLIGHT DTSTART:20300310T030000 RDATE:20301103T010000 TZOFFSETFROM:-0500 TZOFFSETTO:-0400 TZNAME:America/New_York EDT END:DAYLIGHT BEGIN:DAYLIGHT DTSTART:20310309T030000 RDATE:20311102T010000 TZOFFSETFROM:-0500 TZOFFSETTO:-0400 TZNAME:America/New_York EDT END:DAYLIGHT BEGIN:DAYLIGHT DTSTART:20320314T030000 RDATE:20321107T010000 TZOFFSETFROM:-0500 TZOFFSETTO:-0400 TZNAME:America/New_York EDT END:DAYLIGHT BEGIN:DAYLIGHT DTSTART:20330313T030000 RDATE:20331106T010000 TZOFFSETFROM:-0500 TZOFFSETTO:-0400 TZNAME:America/New_York EDT END:DAYLIGHT BEGIN:DAYLIGHT DTSTART:20340312T030000 RDATE:20341105T010000 TZOFFSETFROM:-0500 TZOFFSETTO:-0400 TZNAME:America/New_York EDT END:DAYLIGHT BEGIN:DAYLIGHT DTSTART:20350311T030000 RDATE:20351104T010000 TZOFFSETFROM:-0500 TZOFFSETTO:-0400 TZNAME:America/New_York EDT END:DAYLIGHT BEGIN:DAYLIGHT DTSTART:20360309T030000 RDATE:20361102T010000 TZOFFSETFROM:-0500 TZOFFSETTO:-0400 TZNAME:America/New_York EDT END:DAYLIGHT BEGIN:DAYLIGHT DTSTART:20370308T030000 RDATE:20371101T010000 TZOFFSETFROM:-0500 TZOFFSETTO:-0400 TZNAME:America/New_York EDT END:DAYLIGHT END:VTIMEZONE BEGIN:VEVENT UID:c40b807691c7b07e5addd1494dba2ab7 CATEGORIES:Human and computer vision series:Spring 2007 CREATED:20151203T141541 SUMMARY:Lightness constancy at a slant: high-level, mid-level, and low-level LOCATION:Rutgers University\, FASN-Department of Psychology DESCRIPTION:
When a flat gray surface is rotated in space relati
ve to the light
source, it gets brighter and darker, but continues to ap
pear
approximately the same shade of gray, an example of lightness
co
nstancy. High-level theories associated with Maloney (Boyaci et al,
2004
) and Brainard (Ripamonti et al, 2004) claim that the visual
system achi
eves this by taking into account the direction of the
light source and t
he slant of the surface. Mid-level theories
(Gilchrist et al, 1999) clai
m that the process is much simpler and is
based on luminance ratios betw
een surfaces that face in the same
direction. I will review several line
s of research in which the mid-
level account is tested against both hig
h-level and low-level
(spatial filtering) accounts. The results strongly
support the mid-
level account.
For example, in one critical exp
eriment we used an actual scene
containing blocks resting on the floor,
spheres floating in midair,
attached shadows, cast shadows, glossy highl
ights and luminance
gradients. The target square, always attached
to the middle of the
right-facing side of a large cube, was presented in
different
orientations. The general light source was located to t
he upper
left, except that the cube was shadowed from this light source
and
illuminated by a hidden projector located off to the right. Th
is
gave the right face of the cube a higher luminance than the left
f
ace. Thus, as a target is rotated successively away from the
gener
al light source but its luminance is held constant, the high-
level taki
ng into account theory predicts lower lightness values,
while the relaxe
d coplanar ratio principle predicts darker values.
We found that the tar
get appeared about two Munsell steps darker in
the extreme rotated posit
ion, compared to a position normal to the
general light source.