Transcript Psychonomics (PowerPoint presentation)

Border Elements Deter Shape-from-shadow via Negative Polarity, Not Motion, Not Color
Annual Meeting of the Psychonomic Society, Minneapolis, MN, November 18 – 21, 2004
John M. Kennedy* & Juan Bai
University of Toronto
Lines, Surfaces, and Shadows
Possible Segregations along a Border
Shadow and Dark Line
Color
Percept
Colorand
andShape-from-shadow
Shape-from-shadow Percept
Contour = reflectance change on a surface
A line has two contours, one on each side
We see objects by means of their surfaces, and source of
illumination.
A Hering line added along a shadow border may have impaired
shape-from-shadow perception because of negative polarity of its
contour bordering the shadow.
There are different figure-ground combinations when two regions
share a contour or a line (Kennedy, 1974; Peterson, 1991):
Lines copying surface borders give us surface edge
impressions (e.g., the hill, the roof of the house; adapted
from Kennedy, 1988).
Among the list of 8 possible borders in pictures, only luminance
polarity matters for shadow borders in shape-from-shadow
perception, not stereo (Kennedy & Bai, 2004), and (as shown
here) not color and not motion.
surface borders
a
figure-ground percept along
a contour (adapted from
Rubin, 1915/1958)
b
However, a line copying a shadow border does not give us
the impression of the darkness of the shadow (e.g., the
house’s shadow on the ground; adapted from Kennedy,
1988).
Note that the shadowed area in (b) is darker than the
illuminated region (Cavanagh & Leclerc, 1989), yet shapefrom-shadow perception is diminished.
Hering’s Ringed Shadow
ground-figure-ground
percept along a line
(adapted from Kennedy
et al., 2003)
This favors a perceptual theory (see Cavanagh & Leclerc, 1989)
over figure-ground attention in explaining Hering’s ringed
shadow effect.
b
A red line does not prevent shape-from-shadow perception as
long as the luminance goes dark-to-light from shadow to line and
to non-shadow (a).
figure-groundfigure percepts
along a line
figure-figure percepts
along a line (adapted
from Kennedy et al.,
2003)
In comparison, the same red line blocks shape-from-shadow
perception if it is darker than the shadowed region and hence
creates negative border polarity (b).
Motion and
and Shape-from-shadow
Shape-from-shadow Percept
Motion
Percept
Border-polarity Hypothesis
Kinds of Borders
a
figure-figure percepts along
a contour
But shadows without penumbras (a, adapted from Mooney,
1957) work well in showing a girl’s face, and dark lines in
(b) impair perception of the face.
shadow border
There are 8 kinds of borders that can cause perception of
surfaces, combined from luminance/spectral,
monocular/binocular, and static/moving borders (Kennedy,
Juricevic, & Bai, 2003).
penumbra
c
But lines in (c, adapted from Kennedy, 1993) do not give
us the impression of the dark shadow and the elderly face.
Kennedy, J. M. (1974). A Psychology of Picture Perception. San Francisco:
Jossey-Bass.
Kennedy, J. M. (1988). Paper presented at the Psychonomics Society
Conference, Chicago, IL.
Mooney, C. M. (1957). Canadian Journal of Psychology, 11, 219-226.
Peterson, M. A. (1999). Journal of Experimental Psychology: Human
Perception and Performance, 25, 276-286.
b
c
a
b
c
d
Apparent shadow-border motion resulting from rapid alternations
of (a) and (b) allows shape-from-shadow perception of the
elderly face, possibly due to positive border polarity. This is in
accordance with what the border-polarity hypothesis predicts!
The direction of luminance change can be called ‘polarity.’
b
Hering, E. (1964). Outlines of a Theory of the Light Sense (L. M. Hurvich & D.
Jameson, Trans., pp. 8). Cambridge, MA: Harvard University Press.
(Original work published 1874).
Kennedy, J. M., Juricevic, I., & Bai, J. (2003). In H. Hecht, R. Schwartz, & M.
Atherton (Eds.), Looking into Pictures: An Interdisciplinary Approach
to Pictorial Space (pp. 321-354). Cambridge, MA: MIT Press.
Both negative (a) and Hering-dark-line (b) have negative
contours (i.e., light-to-dark from shadow to non-shadow), and
both fail to show the elderly face in positive (c).
a
Goldstein, B. (2002). Sensation and Perception (6th ed.). Pacific Grove, Calif.:
Wadsworth-Thomson Learning.
Kennedy, J. M., & Bai, J. (2004). Perception, 33, 653-665.
a
Hering (1874/1964) said a shadow with a borderline looks
like a stain. He contended that for a cast shadow (a, after
Goldstein, 2002), shadow perception fails in (b) because
the penumbra is lost to the dark line surrounding the
umbra.
Cavanagh, P., & Leclerc, Y. G. (1989). Journal of Experimental Psychology:
Human Perception and Performance, 15, 3-27.
Kennedy, J. M. & Bai, J. (2000). Perception, 29, 399-407.
Shadow borders are luminance borders that may convey
information about surface shapes, e.g., the elderly face in
(a, adapted from Mooney, 1957), which resembles the
photo in (b).
b
References
Kennedy, J. M. (1993). Drawing and the Blind. New Haven: Yale Press.
umbra
a
Conclusions
It may be the dark line’s negative contour bordering the shadow
in (b) that diminishes shape-from-shadow perception – a ‘borderpolarity’ hypothesis that was supported by Kennedy and Bai
(2000, 2004).
By contrast: The same shadow-border motion resulting from
alternations of negatives (c & d) does not give us the impression
of the same face, possibly due to negative border polarity. This
is again in accordance with what border-polarity predicts!
Rubin, E. (1958). In D. C. Beardslee (Eds.), Readings in Perception (pp. 194203). Princeton, NJ: Van Nostrand. (Original work published 1915).
Acknowledgements
The authors would like to extend special thanks to Humera Iqbal,
Dr. Allison Sekuler, Dr. Paul Muter, Dr. Mark Schmuckler, Dr.
Hiroshi Ono, and Igor Juricevic. We dedicate this poster to Rudolf
Arnheim in honor of his 100th birthday, July 15, 2004.
* [email protected]