Article Figures & Data
Figures
- Figure 1.
Experimental paradigm. A, The eight sequences, each of which was composed of two gratings. Colors were selected so that at sufficiently high presentation frequencies, the two possible color pairs combined to form the same color. B, The relative spatial phases of each successive instance of a given grating were offset by 180°. At sufficiently high presentation frequencies, this yielded a spatially uniform stimulus with no orientation information. C, Examples of orientation choice and of color choice.
- Figure 2.
Probabilistic model for the analysis of data. For details, see Materials and Methods.
- Figure 3.
Results. A, Responses to the four-alternative forced choices illustrated in Figure 1C as a function of grating duration for observer MD. Within each panel, the top left square indicates the percentage of correct responses, the top right square indicates the percentage of conjunction errors, and the bottom quadrant indicates the percentage of feature errors. These percentages are also indicated by the gray scale in each panel, with lower percentages indicated by darker colors. This is shown for the orientation choice and for the color choice. B, Probability of discriminating the colors, orientations, and conjunctions present within a sequence, as a function of grating duration for two observers (top plot for subject MD and bottom plot for subject NJ). Plots show maximum likelihood estimates of the probabilities of discriminating the orientations (green points), the colors (blue points), and the conjunctions (red points) present in a sequence, as inferred from error patterns on the four-alternative forced-choice task. Vertical lines centered on each point indicate 95% confidence intervals on each estimate, as computed using Agresti–Coull interval estimation (Brown et al., 2001). Curves are Weibull function fits (Wichmann and Hill, 2001a) to the estimated probabilities for orientation (green), color (blue), and conjunction (red). The orange line is the product of the probabilities of perceiving the two features, which is the probability of discriminating conjunctions if features were independently discriminated and instantaneously integrated. Asterisks indicate points where pcolor * porientation > pconjunction, p < 0.05. Vertical dashed lines indicate the 75% threshold frequencies for orientation, color, and conjunction. Confidence intervals for thresholds were determined by bootstrap (Wichmann and Hill, 2001b) and are indicated by horizontal bars falling on the 0.75 line. C, Threshold grating durations for orientations, colors, and conjunctions, averaged over 12 observers. The average threshold for orientation is 8.4 ± 1.0 ms (mean ± SEM), for color is 22.9 ± 1.4 ms, and for conjunctions is 32.4 ± 1. 6 ms.
Additional Files
Supplemental Data
Files in this Data Supplement:
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