Color vision in ADHD: part 2--does attention influence color perception?

Abstract

Background: To investigate the impact of exogenous covert attention on chromatic (blue and red) and achromatic visual perception in adults with and without Attention Deficit Hyperactivity Disorder (ADHD). Exogenous covert attention, which is a transient, automatic, stimulus-driven form of attention, is a key mechanism for selecting relevant information in visual arrays.

Methods: 30 adults diagnosed with ADHD and 30 healthy adults, matched on age and gender, performed a psychophysical task designed to measure the effects of exogenous covert attention on perceived color saturation (blue, red) and contrast sensitivity.

Results: The effects of exogenous covert attention on perceived blue and red saturation levels and contrast sensitivity were similar in both groups, with no differences between males and females. Specifically, exogenous covert attention enhanced the perception of blue saturation and contrast sensitivity, but it had no effect on the perception of red saturation.

Conclusion: The findings suggest that exogenous covert attention is intact in adults with ADHD and does not account for the observed impairments in the perception of chromatic (blue and red) saturation.

Figure 1

Appearance task trial sequence. A central fixation (500 ms) was followed by a cue (neutral or peripheral; this study includes both neutral and peripheral cue conditions). After a delay of 53 ms, stimuli were presented for 40 ms. The short period of stimuli presentation precludes saccadic eye movement, which allows for the influence of exogenous covert attention to be assessed. In each trial, participants were instructed to answer the question, "Is the stimulus that looks higher in contrast tilted to the right or left?" or "Is the stimulus that looks more colorful tilted to the right or left?" Participants chose from four options and responded by pressing one of the four designated response keys: left stimulus, tilted to left (‘z’ key); left stimulus tilted to right (‘x’ key); right stimulus, tilted to left (‘n’ key); or right stimulus, tilted to right (‘m’ key). Note that with one key press we got the orientation response, as well as the perceived saturation/contrast (the variable of more interest).

Figure 2

PSE graphs. A) Psychometric functions of color saturation and contrast sensitivity. Data from participants are combined with Weibull functions for each group. Data points are marked with symbols and fitted functions with lines. Each column presents each stimulus (blue, red, contrast). Top row presents psychometric functions for control group, and bottom row for the ADHD group. Horizontal axes represent test stimulus saturation/contrast sensitivity distances in DKL colorspace. Vertical axes are percent of trials for which the test stimulus was selected as more colourful (higher saturation level). Test cued conditions are represented by red lines with circles, neutral cued conditions by black lines with squares, and standard cued conditions by blue lines with triangles. Points of Subjective Equality (PSEs) for the Test shifts to the left for Blue and Contrast indicating that exogenous attention enhanced subjective saturation/contrast sensitivity to be more saturated or higher in contrast than the standard stimuli. Red psychometric functions indicate lack of exogenous attention influence on the stimuli as Test, and Standard psychometric functions are together with Neutral. B) Normalized PSE for color saturation and contrast sensitivity shown in a bar graph. Each participant’s PSEs were normalized by taking the ratio of any one PSE and the average of the test-cued, neutral, and standard-cued PSEs. Each column presents each stimulus (blue, red, contrast). In each bar graph, test cued conditions are represented by a red bar, neutral cued conditions are represented by a black bar, and standard cued conditions are represented by a blue bar. For blue and contrast, when the test stimuli were cued, participants chose the test stimuli when their saturation/contrast levels were lower than those of standard stimuli. This pattern of results indicates that cuing a stimulus increased its perceived blue saturation/ contrast sensitivity level.