Nikolic et al. (2007)

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Current revision as of 15:49, 28 April 2008

Color Opponency in Synaesthetic Experiences

Introduction

The Stroop task asks participants to say the name of the color a word is written in. Time reaction is measured. The challenging thing about this task is that generally the word written is the name of a different color than the color ink it is written in.

Example of a Stroop Task

In this experiment, thte task is attempting to study grapheme color synaesthesia, which is a neurological condition where perceptions of words or numbers are associated with perception of colors. In synaesthetes, the reaction time is decreased if the ink color of the word being read is the same color as the synaesthetic color association (congruent condition). There is a longer reaction time if the two colors are different (incongruent conditions).

There is a neurological explanation for this as discovered through the use of MRI tests. In the brain, certain neurons perceive and process visual stimuli. These neurons have color-opponent fields. For example, cells excited by red are inhibited by green, and the reverse is true. The same situation exists with cells excited by blue and inhibited by yellow.

This study attempts to identify the neural location of these color interactions. A specific Stroop test was created for this study that created incongruent conditions. One task's real color was opponent to the synaesthetic color, and the other had the real color not opposing the synaesthetic color. The hypothesis is that in the opponent incongruent conditions the two colors would involve the same color channels in the brain, and that in the non-opposing incongruent condition the colors would be perceived by different channels. It was hypothesized that it will take participants longer to name the colors that are opponent.

Experiment I

Participants This experiment consisted of 6 synaesthetes, 4 of which were associators (they reported seeing colors on an 'internal screen'. 2 were projectors (seeing colors projected on things they looked at) There were 12 control participants that were not synaesthetic.

Procedure

For each synaesthetic five colors with the highest grapheme-color associations were chosen and used in three conditions. 1. Congruent condition where the color grapheme was the same as the synaesthetic color. 2. Incongruent opponent condition where the color of the graphmem was opposite on the color wheel of the synaesthetic color. 3. Incongruent independent condition where the color of the grapheme and the synaesthetic color were represented by different opponent-color channels. The test took place in a dim room and was administered using a computer. The subjects were asked to state the names of the the colors they saw into a microphone and the time it took for them to say the color was measured.

Results

Results showed that color naming was quicker in the congruent condition than in both the incongruent conditions. In the incongruent conditions significant differences were also found, color naming was quicker in the incongruent independent condition than in the incongruent opponent condition. This suggests that the interference induced by the synaesthetic colors was stronger when the real color of the grapheme was opponent to the synaesthetic color than when it was independent.

Experiment II

The second experiment looked at semantic associations between shape and color. The Stroop tests were generally the same, except that the objects were associated with their normal colors (example- lemons are always associated with yellow). Interferences were expected if the object was colored in an unusual color. The expectation is that these associations are different than the synaesthetic associations and therefore do not involve the previously described opponent-color channels. Four syneasthetes from Experiment I and 8 control subjects participated in the study.

Procedure

The procedure was similar to that of Experiment I, except for the different Stroop task. There were three objects displayed, a heart, lemon and smiley face. Each appeared in three different conditions, presented 25 times each. The three conditions were congruent (yellow lemon), incongruent independent (red lemon), and incongruent opponent (blue lemon).

Results

There appeared to be no difference in performance between the syneasthetes and control subjects. The congruent condition was significantly different than the other two conditions. There was a small different between the incongruent independent and incongruent opponent conditions. There was an average increase in response time of 57ms from the incongruent conditions, as compared to the congruent condition.

General Discussion

Nikolic et al. conclude that the synaesthetic color experiences interfere with the perception and naming of real colors depending if the colors are congruent or incongruent. If the colors are congruent then the response time is much shorter. The interference is much reduced when the two colors are incongruent but not nonopponent (not opposite on the color wheel). Experiment 2 shows that the stronger component reflects synaesthesia and depends on color opponency, (how similar of different the colors are). The weaker component reflects knowledge about synaesthetic associations but it is independent of color opponency.