When checking my ScienceBlogs Brain & Behavior feed this eveninig I came across an interesting post on Neurophilosophy about a new form of synesthesia.
For the uninitiated, Synesthesia is a harmless perceptual condition which causes automatic, uncontrollable associations between different types of perception. For example, in grapheme-color synesthesia, a color is automatically and uncontrollably associated with a number or letter.
The general story here is that the authors are reporting on a new type of synesthesia they call “hearing-motion” synesthesia in which visual stimuli such as short flashes or moving dot patterns automatically generate an auditory percept (such as beeping or tapping). If you’re interested in how the authors (Melissa Saenz and Cristof Koch of CalTech) tested this, I recommend checking out the Neurophilosophy post linked to above, or the (very short) research article in Current Biology.
However, what really intrigues me about this finding is the post-experiment reports that some of my subjects have given. My behavioral experiments generally consist of showing brief (~50-100ms) flashes and asking subjects to compare their durations. I’d say that 10-25% of people I test mention something about using “beeps” or sounds to help them make these judgments. Were these subjects hearing-motion synesthetes?
Not necessarily. There’s a different report from several years ago which argues that the auditory system (the system responsible for much of sound perception) encodes temporal information, while the visual system is more concerned with spatial information. The authors used an interference paradigm to test whether irrelevant auditory or visual information interfered with performance on a rhythm discrimination task. Not surprisingly, they found that extra auditory information impaired performance, but not extra visual information.
So if we use an auditory code to represent temporal information, why don’t we all hear beeps in response to flashes? We know very little about the synesthetes in Saenz & Koch’s experiment. Since the report mentions that this condition has existed for the entire life of each subject, it seems as though musical training can be ruled out as a possible explanation (though out of curiosity I’d still be interested to know each subject’s musical background).
Though I don’t have (m)any readers yet, I’d like to hear if you by chance have hearing-motion synesthesia, or any other thoughts, ideas, or criticisms. Email me (neurotechnica <atsymbol> gmail dot com) or leave a comment here.
Upon looking around some today, I found a few other blogs discussing this finding:
Frontal Blogotomy (disclaimer: I occaisionally contribute to this blog)
The Quantum Pontiff (check out the comments – someone found out they have hearing-motion synesthesia)
Also, a big thanks to NeuroPhilosophy for including NeuroTechnica in a recent roundup of new neuroscience blogs!
2nd Update: Some text of this post was changed after publication. I apologize for any inconvenience this may cause.