Set-size effects for sampled shapes: experiments and model
The location of imperfections or heterogeneities in shapes and contours often correlates with points of interest in a visual scene. Investigating the detection of such heterogeneities provides clues as to the mechanisms processing simple shapes and contours. We determined set-size effects (e.g. sens...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
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Frontiers Media S.A.
2013-05-01
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| Series: | Frontiers in Computational Neuroscience |
| Subjects: | |
| Online Access: | http://journal.frontiersin.org/Journal/10.3389/fncom.2013.00067/full |
| _version_ | 1828222442067197952 |
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| author | Christian eKempgens Gunter eLoffler Harry S. Orbach |
| author_facet | Christian eKempgens Gunter eLoffler Harry S. Orbach |
| author_sort | Christian eKempgens |
| collection | DOAJ |
| description | The location of imperfections or heterogeneities in shapes and contours often correlates with points of interest in a visual scene. Investigating the detection of such heterogeneities provides clues as to the mechanisms processing simple shapes and contours. We determined set-size effects (e.g. sensitivity to single target detection as distractor number increases) for sampled contours to investigate how the visual system combines information across space.Stimuli were shapes sampled by oriented Gabor patches: circles and high-amplitude RF4 and RF8 radial frequency patterns with Gabor orientations tangential to the shape. Subjects had to detect a deviation in orientation of one element (‘heterogeneity’). Heterogeneity detection sensitivity was measured for a range (7-40) of equally spaced (2.3°-0.4°) elements. In a second condition, performance was measured when elements sampled a part of the shapes. We either varied partial contour length for a fixed (7) set-size, co-varying inter-element spacing, or set-size for a fixed spacing (0.7°), co-varying partial contour length.Surprisingly, set-size effects (poorer performance with more elements) are rarely seen. Set-size effects only occur for shapes containing concavities (RF4 and RF8) and when spacing is fixed. When elements are equally spaced, detection performance improves with set-size for all shapes. When set-size is fixed and spacing varied, performance improves with decreasing spacing.Thus, when an increase in set-size and a decrease in spacing co-occur, the effect of spacing dominates, suggesting that inter-element spacing, not set-size, is the critical parameter for sampled shapes. We propose a model for the processing of simple shapes based on V4 curvature units with late noise, incorporating spacing, average shape curvature, and the number of monotonic curvature segments contained in the shape, which accurately accounts for our experimental results, making testable predictions for a variety of simple shapes. |
| first_indexed | 2024-04-12T16:54:38Z |
| format | Article |
| id | doaj.art-63a49cb554b747538e94ca02d0c84a41 |
| institution | Directory Open Access Journal |
| issn | 1662-5188 |
| language | English |
| last_indexed | 2024-04-12T16:54:38Z |
| publishDate | 2013-05-01 |
| publisher | Frontiers Media S.A. |
| record_format | Article |
| series | Frontiers in Computational Neuroscience |
| spelling | doaj.art-63a49cb554b747538e94ca02d0c84a412022-12-22T03:24:17ZengFrontiers Media S.A.Frontiers in Computational Neuroscience1662-51882013-05-01710.3389/fncom.2013.0006748024Set-size effects for sampled shapes: experiments and modelChristian eKempgens0Gunter eLoffler1Harry S. Orbach2Fielmann Akademie Schloss PlönGlasgow Caledonian UniversityGlasgow Caledonian UniversityThe location of imperfections or heterogeneities in shapes and contours often correlates with points of interest in a visual scene. Investigating the detection of such heterogeneities provides clues as to the mechanisms processing simple shapes and contours. We determined set-size effects (e.g. sensitivity to single target detection as distractor number increases) for sampled contours to investigate how the visual system combines information across space.Stimuli were shapes sampled by oriented Gabor patches: circles and high-amplitude RF4 and RF8 radial frequency patterns with Gabor orientations tangential to the shape. Subjects had to detect a deviation in orientation of one element (‘heterogeneity’). Heterogeneity detection sensitivity was measured for a range (7-40) of equally spaced (2.3°-0.4°) elements. In a second condition, performance was measured when elements sampled a part of the shapes. We either varied partial contour length for a fixed (7) set-size, co-varying inter-element spacing, or set-size for a fixed spacing (0.7°), co-varying partial contour length.Surprisingly, set-size effects (poorer performance with more elements) are rarely seen. Set-size effects only occur for shapes containing concavities (RF4 and RF8) and when spacing is fixed. When elements are equally spaced, detection performance improves with set-size for all shapes. When set-size is fixed and spacing varied, performance improves with decreasing spacing.Thus, when an increase in set-size and a decrease in spacing co-occur, the effect of spacing dominates, suggesting that inter-element spacing, not set-size, is the critical parameter for sampled shapes. We propose a model for the processing of simple shapes based on V4 curvature units with late noise, incorporating spacing, average shape curvature, and the number of monotonic curvature segments contained in the shape, which accurately accounts for our experimental results, making testable predictions for a variety of simple shapes.http://journal.frontiersin.org/Journal/10.3389/fncom.2013.00067/fullvisual searchOrientation DiscriminationShape Perceptionsampled shapesshape modelset-size effect |
| spellingShingle | Christian eKempgens Gunter eLoffler Harry S. Orbach Set-size effects for sampled shapes: experiments and model Frontiers in Computational Neuroscience visual search Orientation Discrimination Shape Perception sampled shapes shape model set-size effect |
| title | Set-size effects for sampled shapes: experiments and model |
| title_full | Set-size effects for sampled shapes: experiments and model |
| title_fullStr | Set-size effects for sampled shapes: experiments and model |
| title_full_unstemmed | Set-size effects for sampled shapes: experiments and model |
| title_short | Set-size effects for sampled shapes: experiments and model |
| title_sort | set size effects for sampled shapes experiments and model |
| topic | visual search Orientation Discrimination Shape Perception sampled shapes shape model set-size effect |
| url | http://journal.frontiersin.org/Journal/10.3389/fncom.2013.00067/full |
| work_keys_str_mv | AT christianekempgens setsizeeffectsforsampledshapesexperimentsandmodel AT guntereloffler setsizeeffectsforsampledshapesexperimentsandmodel AT harrysorbach setsizeeffectsforsampledshapesexperimentsandmodel |