The role of segmentation in encoding numerosity D Aagten-Murphy1, V Pisano2, D Burr1 |
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1University of Florence, Italy |
| Humans have a clear sense of the number of elements in a display. However, how segmentation affects numerosity is not well understood. To study segregation we used a sequential 2-AFC task where subjects were presented with a yellow and blue dot display in the first interval, then asked to judge whether there were more or fewer green dots displayed in the second interval. Subjects were cued either before or after the first stimulus whether to base their response on the number of yellow, blue or total dots. We tested 8 different blue/yellow colour ratios and 4 different total dot numerosity/densities. The results show that when judging the total number of dots, subjects accurately compare magnitudes, regardless of cue condition. However, when pre-cued for an individual colour, subjects substantially overestimated displays with large distracter ratios. In contrast, when post-cued, subjects underestimated individual features quantities up to 30%, with the maximum underestimation occurring for equal numbers of target and distracter. Overall the results suggest that numerosity displays are automatically processed as a single grouped display, with multiple features interfering in the estimation of numerosity, in a way that depends on whether subjects are required to segment the display visually or from memory. |
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