When do three sticks become the letter “A”?
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1
Simon Fraser University, Canada
“To the uneducated, the letter ‘A’ is just three sticks.” This amusing statement made by Eeyore in a classic Winnie-the-Pooh storybook (A.A. Milne) seems obvious but what happens in the brain when the three sticks form the perception of a letter ‘A'? Many studies have identified regions within human ventral visual stream to be important for object identification and categorization; however, knowledge of how perceptual information is communicated within the visual network is still limited. Current theories on object identification posit that incoming perceptual information about an object is matched to internal representations. If there is a high correspondence then the object is identified, if there isn’t then the object requires more detailed processing. This extra processing should manifest as additional activity and neural communication amongst multiple cortical regions. I examined this by using time-frequency and functional connectivity analyses of brain source data estimated from MEG recordings. I found that, as compared to familiar letters, unfamiliar letter-like characters (pseudoletters) elicited significantly prolonged gamma-band (50-80 Hz) activity and delayed communication between 245-375 ms amongst regions in a more distributed visual network. I also found that viewing letters produced alpha-band (9-12 Hz) desynchronization and gamma-band synchronization as early as 85 ms that wasn’t evident when viewing pseudoletters. The right fusiform gyrus was a central hub of connectivity in both frequency bands, thereby illustrating the concept that neural regions decrease communication within one network while increasing it in another. These findings indicate that familiar object processing begins by at least 85 ms and doesn’t persist as long as that for unfamiliar object processing. Moreover, the extra activity and distributed communication for pseudoletters might reflect perceptual binding of their novel line configurations in order to begin consolidating them into unitized templates used on subsequent viewings.
Conference:
Biomag 2010 - 17th International Conference on Biomagnetism , Dubrovnik, Croatia, 28 Mar - 1 Apr, 2010.
Presentation Type:
Poster Presentation
Topic:
Language
Citation:
Herdman
A
(2010). When do three sticks become the letter “A”?.
Front. Neurosci.
Conference Abstract:
Biomag 2010 - 17th International Conference on Biomagnetism .
doi: 10.3389/conf.fnins.2010.06.00277
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Received:
01 Apr 2010;
Published Online:
01 Apr 2010.
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Correspondence:
Anthony Herdman, Simon Fraser University, Burnaby, Canada, atherdma@sfu.ca