Kim et al. (2006)

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Revision as of 02:59, 28 April 2008

In 2006, Chai-Youn Kim, Randolph Blake, and Thomas J. Palmeri ran two experiments on subjects with graphemic synesthesia to determine whether or not the synesthetically induced color that these individuals experience behaves just like real colors.

Through previous experiments in figure grouping, visual search, and orientation-contingent color aftereffects, researchers have verified the existence of real synesthetic experiences. However, up until this experiment, there had been few if any experiments designed to detect the differences between real color behavior and synesthetic color behavior, and how the two interact.

For instance, graphemic synesthetes readily report the color of a green letter, even when that letter’s synethetically induced color may be red. One might expect that the two colors would blend, yet these synesthetes describe the colors as if overlaying each other. Yet at the same time, we know that the two color forms can interact in what experimenters call the synesthetic stroop test. Basically, the synesthetically induced colors of a character interfere to reduce the efficiency by which a synesthete names the actual colors of letters.

In this experiment, researchers pursued the interaction question by utilizing previously documented grouping effects from real colors, and attempting to replicate these effects with synesthetically-induced colors. For this, experimenters used two patients under the “projector” subtype of synesthete, where synthetically induced colors are seen directly on the corresponding characters and not in the “mind’s eye.”

Using two projector type synesthetes, WO and LR, experimenters first ran a bistable Apparent Motion (AM) test to study the role of synesthetic color grouping over time. AM is an illusion produced by rapidly switching the presentation of two overlaying frames, each with fixed tokens located at strategic positions. To visualize the effect, one can imagine a flip book that has only two different alternating pictures in it, with each picture displaying four tokens in different locations. If the tokens are located properly, the presentation of the two frames in rapid succession will induce an optical illusion of either clockwise (CW) or counterclockwise (CCW) rotation of the tokens. The type of rotation more likely for the observer to see can be manipulated by how far corresponding tokens of frame one and frame two are spaced. An even better instrument for creating the illusion is color. For instance, a green token in frame one will appear to move to the position of a different green token in frame two, even if a corresponding red or achromatic token is closer. Experimenters use this idea to test whether or not synesthetic colors will also affect a synesthete’s perception of apparent motion. Since color has such a powerful ability to influence perceptual grouping over time in bistable AM, it affords experimenters an opportunity to study possible interactions between real and synesthetic colors.

The experimenters compared controls vs. synesthetes in four conditions: control, synesthetic, interaction, and real.

Control- frames 1 and 2 consisted of pairs of achromatic and non-synesthetic inducing characters.

Synesthetic- frames 1 and 2 contained two pairs of achromatic alphabetic characters, and in each frame one pair of characters induced one synesthetic color (red) and the other pair induced a different synesthetic color (blue).

Interaction- two pairs of physically colored and non-synthetic color inducing characters were presented in frame 1 and two different pairs of achromatic, synthetic color inducing characters with matching synesthetic colors were presented in frame 2.

Real- two pairs of physically colored, non-synthetic color inducing characters were presented in frame 1 and two different pairs of physically colored, non-synthetic color inducing were presented in frame two.

Observers pressed a key to initiate the trial, and reported the perceived direction of motion by pressing on e of two buttons. The four conditions were ran in 350 trial blocks with randomly varying pathlengths.

Both LR and WO experienced the illusion of motion in the synthetic trials, whereas the controls experienced none. This indicates that synthetic colors can behave like real colors, at least in regards to AM. Similarly, and even more remarkable, was the fact that LR and WO experienced perceived motion in the interaction trials, where only one frame is colored. This means that the real colors of frame one did in fact interact with the synthetic colors induced from characters on the other frame.

For some reason, WO experienced no perception of bistable AM in the real condition.