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. 2022 Sep 15;17(9):e0274564.
doi: 10.1371/journal.pone.0274564. eCollection 2022.

Spatial and chromatic properties of numerosity estimation in isolation and context

Elena Gheorghiu  1 , Dirk Goldschmitt  1
Affiliations

Spatial and chromatic properties of numerosity estimation in isolation and context

Elena Gheorghiu et al. PLoS One. .

Abstract

Numerosity estimation around the subitizing range is facilitated by a shape-template matching process and shape-coding mechanisms are selective to visual features such as colour and luminance contrast polarity. Objects in natural scenes are often embedded within other objects or textured surfaces. Numerosity estimation is improved when objects are grouped into small clusters of the same colour, a phenomenon termed groupitizing, which is thought to leverage on the subitizing system. Here we investigate whether numerosity mechanisms around the subitizing range are selective to colour, luminance contrast polarity and orientation, and how spatial organisation of context and target elements modulates target numerosity estimation. Stimuli consisted of a small number (3-to-6) of target elements presented either in isolation or embedded within context elements. To examine selectivity to colour, luminance polarity and orientation, we compared target-only conditions in which all elements were either the same or different along one of these feature dimensions. We found comparable performance in the same and different feature conditions, revealing that subitizing mechanism do not depend on 'on-off' luminance-polarity, colour or orientation channel interactions. We also measured the effect of varying spatial organisation of (i) context, by arranging the elements either in a grid, mirror-symmetric, translation-symmetric or random; (ii) target, by placing the elements either mirror-symmetric, on the vertices of simple shapes or random. Our results indicate higher accuracy and lower RTs in the grid compared to all other context types, with mirror symmetric, translation and random arrangements having comparable effects on target numerosity. We also found improved performance with shape-target followed by symmetric and random target arrangements in the absence and presence of context. These findings indicate that numerosity mechanisms around the subitizing range are not selective to colour, luminance polarity and orientation, and that symmetric, translation and random contexts organisations inhibit target-numerosity encoding stronger than regular/grid context.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Example stimuli used in Experiments 1–3.
Stimuli consisted of a small number of elements (3, 4, 5 or 6) positioned either (a) on the vertices of simple shapes, e.g., equilateral triangle, square, pentagon and hexagon or (c) random, e.g., elements placed randomly anywhere within and including the virtual contour-path except on the vertices. (b) Equilateral triangle sampled by either 3, 4, 5 or 6 elements, with three elements always positioned on the vertices and the remaining elements placed randomly anywhere within and including the virtual contour-path. (d) Stimuli made of different luminance-polarity elements (white and black). Elements had either same (a,c) or different (d) luminance-polarity (Experiment 2), and either same or different (b) colour (Experiment 1). (e,f) Experiment 3 stimuli made of Gabor elements oriented either (e) collinear or (f) orthogonal to the virtual path of simple contour shapes. For all experiments, the orientation of each virtual shape configuration was randomized from trial to trial.
Fig 2
Fig 2. Experiment 4 stimuli.
Achromatic dot patterns made of 36 elements that were divided into target (either 3, 4, 5 or 6) and context elements. The target elements were placed either (a) random, (b) mirror symmetric, or (c) on the vertices of simple geometric shapes (equilateral triangle, square, pentagons, hexagon). Context elements were organised either mirror symmetric (top), translation symmetric (2nd row), randomly (3rd row) and in a regular grid (bottom). Note that the combination of shape target—grid context was not used as placing target elements on the vertices of simple shapes (triangle, pentagon, hexagon) within a grid would break the regularity of the grid pattern. (d) Schematic representation of the procedure.
Fig 3
Fig 3. Experiment 1 results (effect of colour).
(a) Accuracy and (b) reaction time are plotted as a function of number of elements for simple shape (left side of each panel) and random (right side of each panel) configurations, and for same (blue/green symbols) and different (red/purple symbols) colour conditions. Top to bottom panels correspond to different simple shape configurations: Equilateral triangle (top panel), square, pentagons and hexagon (bottom panel) configuration. The error bars indicate standard error of the mean (±1 SEM).
Fig 4
Fig 4. Experiment 2 results (effect of luminance polarity).
(a) Accuracy and (b) reaction time are plotted as a function of number of elements for simple shape (left side of each panel) and random (right side of each panel) configurations, and for same (blue/green symbols) and different (red/purple symbols) luminance poalrity conditions. Top to bottom panels correspond to different simple shape configurations: Equilateral triangle (top panel), square, pentagons and hexagon (bottom panel) configuration. The error bars indicate standard error of the mean (±1 SEM).
Fig 5
Fig 5. Experiment 3 results (effect of orientation).
(a) Accuracy and (b) reaction time are plotted as a function of number of elements for simple shape (left side of each panel) and random (right side of each panel) configurations, and for colinear (blue/green symbols) and orthogonal (red/purple symbols) to contour-path orientation conditions. Top to bottom panels correspond to different simple shape configurations: Equilateral triangle (top panel), square, pentagons and hexagon (bottom panel) configuration. The error bars indicate standard error of the mean (±1 SEM).
Fig 6
Fig 6. Experiment 4 results (context effects).
(a) Accuracy and (b) reaction time are plotted as a function of number of elements and context configuration (no context, grid, mirror symmetric, translation, random), for different type of target arrangements: Random target (top panels), symmetric target (middle panels) and shape target (bottom panel). The error bars indicate standard error of the mean (±1 SEM).
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