Papers selected by Masami Ikeda

　　　■On the perception of shape from shading.
　　　■Search for feature and for relative position: Measurement of capacity limitations.
　　　■Preattentive perception of elementary three-dimensional shapes.
　　　■Psychophysical evidence for boundary and surface systems in human vision.
　　　■Effects of static textured background on motion integration.
　　　■Psychophysical evidence for boundary and surface systems in human vision.
　　　■Evidence for boundary-specific grouping.

On the perception of shape from shading.

Kleffner, Dorothy A.; Ramachandran, V. S.
U California-San Diego, La Jolla, US
Perception & Psychophysics. 1992 Jul Vol 52(1) 18-36

Five experiments with 38 adults examined the manner in which the perception of shape from shading interacts with other visual processes such as perceptual grouping, preattentive search ("pop-out"), and motion perception. Findings indicate that the extraction of shape from shading information incorporates at least 2 assumptions: (1) that there is a single light source illuminating the whole scene and (2) that the light is shining from "above" in relation to retinal coordinates. Tokens defined by shading can serve as a basis for perceptual grouping and segregation. The reaction time (RT) for detecting a single convex shape does not increase with the number of items in the display. This "pop-out" effect must be based on shading rather than on differences in luminance polarity.

Search for feature and for relative position: Measurement of capacity limitations.

Poder, Endel
Tallinn Pedagogical U, Lab of Cognitive Neuroscience, Tallinn, Estonia
Vision Research. 1999 Apr Vol 39(7) 1321-1327

Examined the effect of the set size on the accuracy of the visual search using 2 types of stimuli: (1) target deviates from distracters by the relative position of its elements only; and (2) target deviates from distracters by the presence/absence of simple features. 4 observers (aged 17-48 yrs) served as participants. The results indicate that a search for targets defined by relative position in the set of line drawing type of stimuli is fundamentally different from a search for more simple (feature) stimuli and may conform to a strict capacity limited model.

Preattentive perception of elementary three-dimensional shapes.

Sun, Jennifer Y.; Perona, Pietro
California Inst of Technology, Pasadena, CA, US
Vision Research. 1996 Aug Vol 36(16) 2515-2529

Measured 3-dimensional (3-D) pop-out with an experimental paradigm that involved controlled display times and masking. Five adults served as Ss. Experiments in which a single target pattern was discriminated from multiple background distractors show that shaded 2-D stimuli consistent with a top-lit polyhedral interpretation were processed fast (<80 msec) and in parallel. Unshaded line drawings of the same shapes, however, were processed serially. Strong pop-out asymmetries and control experiments involving shaded patterns that did not have familiar 3-D interpretations suggest that such fast parallel processing is dependent on perception of 3-D shape. Furthermore, this process can be influenced by contextual scene information, in a manner that is dependent on whether or not the additional cues contribute to the perception of a consistent 3-D scene.

Psychophysical evidence for boundary and surface systems in human vision.

Rogers-Ramachandran, Diane C.; Ramachandran, V. S. U
California San Diego, Brain & Perception Lab, La Jolla, CA, US
Vision Research. 1998 Jan Vol 38(1) 71-77

Presents psychophysical evidence for the existence of 2 distinct systems in human vision: a fast, sign-invariant system dealing with extracting contours and a slower, sign-sensitive system dealing with assigning surface color. A class of stimuli has been developed which seems to selectively activate the fast, contour system. The stimulus is formed by adjacent fields of black and white spots, which flicker in counterphase at 15 Hz, on a uniform gray field. The 6 naive Ss cannot discriminate the temporal phase relationship between the fields of spots; still, they can see a "phantom contour" separating the 2 indiscriminable fields. The surface characteristics can only be seen when the stimulus is significantly slower. Also, phantom contours disappear with equiluminant spots but can be seen with very low contrast spots, and are enhanced with peripheral viewing. Overall, the results suggest that the fast contour-extracting system may be the magnocellular system or a magno-recipient area.

Effects of static textured background on motion integration.

Lorenceau, Jean; Boucart, Muriel
Vision Research. 1995 Aug Vol 35(16) 2303-2314

Examined the influence of a static texture background on motion integration, and tested whether high level (semantic) information could interact with motion integration. A series of experiments were conducted to determine the effects of contrast, relative contrast and motion onset asynchrony (MOA), element density, and "local texture" on 10 Ss, who viewed the display binocularly from 114 cm, and reported their clockwise and counterclockwise decision. Results indicate that integration of local motion signals into a global direction is modulated by the contrast and density of a static texture surrounding the motion signals. With figures at high contrast, the presence of a texture enhanced direction discrimination, while at low contrast it was impaired. The effects of the texture, either facilitation or suppression increased with texture contrast. Accuracy improved with MOA and decreased with texture density.

Psychophysical evidence for boundary and surface systems in human vision.

Rogers-Ramachandran, Diane C.; Ramachandran, V. S.
Vision Research. 1998 Jan Vol 38(1) 71-77 Evidence for boundary-specific grouping.

Presents psychophysical evidence for the existence of 2 distinct systems in human vision: a fast, sign-invariant system dealing with extracting contours and a slower, sign-sensitive system dealing with assigning surface color. A class of stimuli has been developed which seems to selectively activate the fast, contour system. The stimulus is formed by adjacent fields of black and white spots, which flicker in counterphase at 15 Hz, on a uniform gray field. The 6 naive Ss cannot discriminate the temporal phase relationship between the fields of spots; still, they can see a "phantom contour" separating the 2 indiscriminable fields. The surface characteristics can only be seen when the stimulus is significantly slower. Also, phantom contours disappear with equiluminant spots but can be seen with very low contrast spots, and are enhanced with peripheral viewing. Overall, the results suggest that the fast contour-extracting system may be the magnocellular system or a magno-recipient area.

Evidence for boundary-specific grouping.

Elder, James H.; Zucker, Steven W.
Vision Research. 1998 Jan Vol 38(1) 143-152

Examined the separate influence of region and boundary cues on perceptual grouping of form using 2-dimensional concave and convex images on 11 Ss. Artificial images of fragmented outline figures and sparse textures were used to test the visual search and closure effects on shape recognition, discrimination and identification in discrimination and recognition tasks. Results showed that closed images require less visual processing than open images, suggesting an attentional element in boundary cuing which is not apparent in texture perception. The findings show that boundary cues such as contours are used in perceptual grouping early in the stages of visual processing and that the interaction of region elements such as texture segmentation come into play later.