A standardized test battery for the study of synesthesia

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Abstract

Synesthesia is an unusual condition in which stimulation of one modality evokes sensation or experience in another modality. Although discussed in the literature well over a century ago, synesthesia slipped out of the scientific spotlight for decades because of the difficulty in verifying and quantifying private perceptual experiences. In recent years, the study of synesthesia has enjoyed a renaissance due to the introduction of tests that demonstrate the reality of the condition, its automatic and involuntary nature, and its measurable perceptual consequences. However, while several research groups now study synesthesia, there is no single protocol for comparing, contrasting and pooling synesthetic subjects across these groups. There is no standard battery of tests, no quantifiable scoring system, and no standard phrasing of questions. Additionally, the tests that exist offer no means for data comparison. To remedy this deficit we have devised the Synesthesia Battery. This unified collection of tests is freely accessible online (http://www.synesthete.org). It consists of a questionnaire and several online software programs, and test results are immediately available for use by synesthetes and invited researchers. Performance on the tests is quantified with a standard scoring system. We introduce several novel tests here, and offer the software for running the tests. By presenting standardized procedures for testing and comparing subjects, this endeavor hopes to speed scientific progress in synesthesia research.

Introduction

For the past century, synesthesia research has fought an uphill battle against the perceived subjectivity of the phenomenon. Examining the reality of these synesthetic experiences has been a goal of many researchers over the past decade (Baron-Cohen and Harrison, 1997, Cytowic, 1998, Hubbard and Ramachandran, 2003). To this end, several tests have been devised to objectively quantify a personal experience. For example, some tests distinguish synesthetes from controls by testing the consistency of synesthetic associations across multiple trials over varying periods of time (Asher et al., 2006, Baron-Cohen et al., 1996). Additionally, questionnaires have been developed to collect detailed information about personal synesthetic experience (Grossenbacher, personal communication; Hubbard and Ramachandran, personal communication; Rich et al., 2005, Ward and Simner, 2003; also see http://www.synaesthesia.uwaterloo.ca/ColorAssessment.htm, described in Smilek et al., 2005).

However, there currently exists no standardized method for presenting tests, quantifying scores and phrasing questions, as well as no ready access to the tests and their results for comparing across synesthetes. In an attempt to remedy this deficit, we have developed an online research toolbox, the Synesthesia Battery (available at http://www.synesthete.org). This battery hopes to provide a standard for the community of synesthetes and researchers. It envisages faster scientific progress by allowing comparison and pooling of data across laboratories. The software tests are offered both online and as a downloadable collection of platform-independent MATLAB programs, both freely available at http://www.synesthete.org.

Section snippets

The synesthesia battery

The first of its kind, the synesthesia battery is a web-based, online information and testing portal. On entering http://www.synesthete.org, participants register and then sign in with a password which restricts access to their data. During the process, they are given the option to enter a researcher's email address, allowing them to privately share their test results with only that researcher. Through this mechanism, researchers worldwide can send their subjects to this website for later

Questionnaire

The online questionnaire consists of 80 questions and requires an average of 10 min to complete, depending on the forms of synesthesia experienced by the participant. The battery begins with a screen asking whether the person believes they have any of a numbers of variants of synesthesia (20 possible choices, with a textbox for any other variants not listed). Their answers on the first screen automatically direct which parts of the questionnaire they will see and which tests they will take. The

Grapheme-color consistency test

One of the most prevalent forms of synesthesia – and the most readily studied using Internet technology – is the triggering of color experience by graphemes (letters and digits; Baron-Cohen et al., 1993, Day, 2005, Simner et al., in press). It has been previously reported that grapheme-color synesthetes show greater matching consistency than non-synesthetes—that is, when asked to match colors to graphemes, and then re-tested some time later, they are largely consistent in their matches (Asher

A new measure: the speeded congruency test

There still exists the possibility that a person could cheat on the color consistency test by constructing an arbitrary code or ‘cheat-sheet’ that translates graphemes into colors (an undergraduate student of the author's did this one summer, with great success). Especially since there is no time pressure on the responses, such cheating would be difficult to detect.

To preclude this possibility, we have devised a new kind of test that is administered to participants as soon as they have

The effect of grapheme contrast on synesthetic colors: separating ‘lower’ from ‘higher’ synesthetes?

One case study has previously reported that lowering the contrast of a digit can change or eliminate the synesthetic color association (Hubbard et al., 2006). We have developed a variation of the grapheme-color test which presents letters and digits to subjects at seven different levels of contrast from high (black grapheme against a white background, or vice versa) to low (a gray grapheme just slightly different from a gray background). Subjects use the color palette described above to choose

Other tests in the battery

In variations on this theme, we have developed other online tests, including those that match colors to weekdays and months (Fig. 4). Other tests in development include comparing colored weekdays in English, Spanish and foreign alphabets, and the presentation of moving stimuli with the ability to choose matching synesthetic pitches, for those with motion  sounds synesthesia. The battery has been constructed with a flexible framework for continued development. As new tests are added, researchers

Password-protected access to test results

On completion of all the applicable tests, a comprehensive results page is automatically generated. These results can be viewed while logged in to the site or can be securely accessed at any later date by the participant or the researcher named by the participant. No one else will have access to the results. Researchers whose subjects have taken the battery have an automatically generated, password-protected personalized page that shows a list of all their subjects, complete with completion

Discussion

To enhance the rigor and global accessibility of synesthesia testing, we have developed the synesthesia battery, an online collection of tests designed to study and phenotype synesthesia. The battery is free and open to the public. It is built to grow with new discoveries and user input. The battery is intended to standardize and speed synesthesia research, as well as to open up testing to laboratories around the globe.

The battery has been designed to be user friendly and intuitive. Researchers

Acknowledgments

The authors thank Drs. Edward Hubbard and Vilayanur Ramachandran for an early version of the questionnaire, Brian Rosenthal for programming help and advice, and Drs. Julia Simner, Edward Hubbard and Richard Cytowic for feedback on the manuscript.

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