Adaptation and visual salience

Abstract

We examined how the salience of color is affected by adaptation to different color distributions. Observers searched for a color target on a dense background of distractors varying along different directions in color space. Prior adaptation to the backgrounds enhanced search on the same background while adaptation to orthogonal background directions slowed detection. Advantages of adaptation were seen for both contrast adaptation (to different color axes) and chromatic adaptation (to different mean chromaticities). Control experiments, including analyses of eye movements during the search, suggest that these aftereffects are unlikely to reflect simple learning or changes in search strategies on familiar backgrounds, and instead result from how adaptation alters the relative salience of the target and background colors. Comparable effects were observed along different axes in the chromatic plane or for axes defined by different combinations of luminance and chromatic contrast, consistent with visual search and adaptation mediated by multiple color mechanisms. Similar effects also occurred for color distributions characteristic of natural environments with strongly selective color gamuts. Our results are consistent with the hypothesis that adaptation may play an important functional role in highlighting the salience of novel stimuli by discounting ambient properties of the visual environment.

Figure 1

Examples of a highly conspicuous (left) or inconspicuous target on color backgrounds defined by chromatic variations along the LvsM axis.

Figure 2

Target and background colors used in the search task. Each image shows examples of the target chromaticities against one of the 4 backgrounds that each varied along a single axis in the chromatic plane. Target chromaticities spanned a range of angles and contrasts in the plane (filled circles in the diagram) while backgrounds uniformly sampled contrast along one angle in the plane (lines in the diagram).

Figure 3

Search times for a single observer on each of the 4 backgrounds. Each plot shows the reaction times as a function of the distance of the target from the background axis. Search times on each background are shown after adaptation to (a) the same background (red circles), (b) the orthogonal color background (blue triangles), or (c) a uniform field (black squares). Lines show the search times when the targets were instead shown on backgrounds that varied only in luminance.

Figure 4

Relative search times on the 4 chromatic backgrounds. Symbols in each panel plot the difference in response times between neutral adaptation and adaptation to the same background (red circles) or orthogonal background (blue triangles) for 3 observers.

Figure 5

Comparison of search times for targets shown on the bluish-yellowish (135–315 deg) background (red circles) or magenta-greenish (45–225) background (blue triangles) following adaptation to the uniform field. Solid and dashed lines plot search times for the corresponding targets on the achromatic backgrounds. The three panels show results for three observers.

Figure 6

Target and background colors used for testing search for different luminance and chromatic axes. Each image shows examples of the target stimuli against one of the 4 backgrounds that each varied along a single axis in the Luminance and LvsM plane.

Figure 7

Search times for a single observer on each of the 4 color–luminance backgrounds. Each plot shows the reaction times as a function of the distance of the target from the background axis. Search times on each background are shown after adaptation to (a) the same background (red circles), (b) the orthogonal color background (blue triangles), or (c) a uniform field (black squares). Lines show the search times when the targets were instead shown on uniform fields.

Figure 8

Relative search times on the 4 color–luminance backgrounds. Symbols in each panel plot the difference in response times between neutral adaptation and adaptation to the same background (red circles) or orthogonal background (blue triangles) for 3 observers.

Figure 9

Coordinates of the targets and background colors used to assess the effects of adaptation to the mean chromaticity on color search.

Figure 10

Backgrounds that vary in contrast along the same axis as the mean color shift, and thus orthogonal to the axis that distinguishes the target from the background.

Figure 11

Backgrounds that vary in contrast along axes perpendicular to the mean color shift.

Figure 12

Search times for a single observer on each of the 8 backgrounds with a mean color shift. Top 4 panels: Background axes that are parallel to the shift in mean color (Figure 10). Bottom 4 panels: Background axes that are perpendicular to the direction of mean color shift (Figure 11). Each plot shows the reaction times as a function of the distance of the target from the background axis. Search times on each background are shown after adaptation to the mean color of the background (red circles) or to the complementary color (blue triangles).

Figure 13

(a) Radial or (b) rectangular grid of coordinates for target colors used in the search tasks in which eye movements were monitored.

Figure 14

Eye movement patterns for one observer for target search on the (left column) LvsM or (right column) SvsLM background. Top row: Search times vs. target contrast after adaptation to the LvsM background (red circles) or SvsLM background (blue circles). Second row: Number of fixations as a function of target contrast. Third row: Average fixation duration as a function of contrast. Bottom row: Saccade amplitude vs. contrast.

Figure 15

Target and background coordinates for color search on the nonselective color background.

Figure 16

Average search times as a function of the color axis for targets presented on the nonselective background, after adaptation to the background (red circles) or a uniform field (blue triangles). The three panels show results for three observers.

Figure 17

Search times for targets sampled from the rectangular stimulus grid, as a function of the (left column) LvsM or (right column) SvsLM contrast of the targets. Search times are shown after adaptation to the background axis (red circles) or the orthogonal axis (blue triangles). Lines plot the fits of Gaussian functions to the search times. Top and middle panels: Results for two observers searching on the LvsM background. Bottom panels: Results for a third observer tested on the SvsLM background.

Figure 18

Color distribution (red circles) from an (top) arid or (bottom) lush scene used to define the colors of the backgrounds, and the set of target colors (blue triangles). The distribution colors are plotted as contrasts along the different pairs of cardinal axes.

Figure 19

Examples of the backgrounds defined by the (left) arid or (right) lush color environment.

Figure 20

Search times as a function of signal-to-noise ratio for targets presented against the arid (red circles) or lush (blue triangles) background. The three panels show results for three observers.

Figure 21

Search times on the (left columns) arid or (right column) lush background following adaptation to samples from the background (red circles) or to uniform fields (blue circles). Rows plot the results for 3 observers.