Beyond Correlation: Do Color Features Influence Attention in Rainforest?

Abstract

Recent research indicates a direct relationship between low-level color features and visual attention under natural conditions. However, the design of these studies allows only correlational observations and no inference about mechanisms. Here we go a step further to examine the nature of the influence of color features on overt attention in an environment in which trichromatic color vision is advantageous. We recorded eye-movements of color-normal and deuteranope human participants freely viewing original and modified rainforest images. Eliminating red–green color information dramatically alters fixation behavior in color-normal participants. Changes in feature correlations and variability over subjects and conditions provide evidence for a causal effect of red–green color-contrast. The effects of blue–yellow contrast are much smaller. However, globally rotating hue in color space in these images reveals a mechanism analyzing color-contrast invariant of a specific axis in color space. Surprisingly, in deuteranope participants we find significantly elevated red–green contrast at fixation points, comparable to color-normal participants. Temporal analysis indicates that this is due to compensatory mechanisms acting on a slower time scale. Taken together, our results suggest that under natural conditions red–green color information contributes to overt attention at a low-level (bottom-up). Nevertheless, the results of the image modifications and deuteranope participants indicate that evaluation of color information is done in a hue-invariant fashion.

Visual search in natural scenes explained by local color properties

“…The factors determining visual search in natural scenes are relatively poorly understood, but it has been generally assumed that local color properties are not strong determiners of performance [24,25,[44][45][46]. As has been shown here, however, local values of lightness and the two chroma components can explain 57-60% of the variance in observers' detection performance, averaged over scenes.…”

“…Again with free viewing, different patterns of fixations have been reported [24,25] with colored and gray-level versions of the same natural scenes. Nevertheless, the influence of local color properties on search performance remains unclear [cf., 26,27].…”

Effects of salience are both short- and long-lived

“…This view could potentially explain the delayed effect of salience on saccadic likelihood as a consequence of decision-makers employing a decision strategy that varies in its sensitivity to bottom up influences. One might, for instance, imagine that decision strategies that favor exploration over exploitation would benefit from openness to bottom up processes particularly in environments where salience is correlated with utility or validity (Anderson et al, 2011;Frey et al, 2011). Strategies favoring exploitation would on the other hand benefit from strong top down control thereby minimizing distractions due to bottom up influences.…”

Influence of local scene color on fixation position in visual search

“…In free viewing, patterns of fixations have been reported as being different between colored and gray-scale images of natural scenes [25,27], and in some specific discrimination tasks, the role of color can be decisive, such as in discriminating fruit and fresh foliage from more mature foliage [28,29]. But the general importance of local scene color on gaze behavior in visual search is unclear.…”

“…Among natural scene properties explaining gaze behavior, color has received relatively little attention, for instance in [8][9][10]13,14,19,22,23], although see [16,[24][25][26]. In free viewing, patterns of fixations have been reported as being different between colored and gray-scale images of natural scenes [25,27], and in some specific discrimination tasks, the role of color can be decisive, such as in discriminating fruit and fresh foliage from more mature foliage [28,29].…”