Melissa Saenz, Ph.D.|
Postdoctoral Fellow in Biology, Koch Lab
Lecturer in Computation & Neural Systems
Caltech, MC 216-76
Pasadena CA 91125
New Caltech Course on Brain Plasticity
I am pleased to teach BI/CNS 286. [course website].
Sight Recovery after Blindness
|We studied brain reorganization in two individuals who had been blind since early childhood and whose vision was partially restored as adults in their 40's. Using functional MRI brain scans, we found that a specific region of their visual cortex (MT+), which normally responds to visual motion, responded to both sound motion and visual motion in the sight-recovery subjects. It was previously known that the visual cortex of blind persons can take on non-visual functions (cross-modal brain plasticity). Our study tells us that this brain reorganziation didn't occur randomly, but rather took advantage of MT+'s specialization for motion processing. It also tells us that the sound responses didn't go away once vision was restored, but persisted together with regained visual responses even after many years.
Saenz, Lewis, Huth, Fine, Koch (2008) Visual Area MT+ Responds to Auditory Motion in Human Sight-Recovery Subjects. Journal of Neuroscience. [pdf]
News Coverage: Nature News, Science News, New Scientist, Caltech Press Release, Dana Foundation
A competitive blind soccer player tracks the sound of a moving, ringing ball.
Discovery of Auditory Synesthesia
|We discovered an unusual sensory experience in otherwise normal people who hear sounds when they see visual flashes or visual motion. This demonstrates a previously undescribed form of synesthesia, a benign neurological condition involving cross-activation of the senses. As objective evidence, "hearing-motion synesthetes" performed much better than control subjects at identifying rhythmic patterns of visual flashes that were similar to visual Morse code signals. Synesthetes had an advantage because they not only saw, but also heard the visual patterns. Hearing-motion synesthesia could be useful for studying how the auditory and visual processing systems interact in the brain.
Surprisingly, it was not difficult to find people with hearing-motion synesthesia once we knew what to ask! The sound perceptions are simple in nature (such as beeping, tapping, whirring) and non-linguistic.
Saenz and Koch (2008) The Sound of Change: Visually-induced auditory synesthesia. Current Biology. [pdf]
News Coverage: Nature News, Commentary in Current Biology, New Scientist, BBC News, Scientific American Mind, Caltech Press Release, Spektrumdireckt (German), ABC News, MSNBC, MSN Health, YouTube.
Video News coverage at ScienCentral.
Some people hear a sound when viewing this movie. Do you?
"Global" Visual Attention
More visual information reaches our eyes than our brains can fully process. As William James wrote "My experience is what I agree to attend to. Only those items which I notice shape my mind - without selective interest, experience is utter chaos."
(Principles of Psychology, 1890). My experiments tested the hypothesis that attention to certain basic visual features (e.g. color, motion direction) in one location modulates neuronal responses throughout the visual scene. For example, when an observer searches a shelf for a red book, attention would sensitize neurons tuned to the color red with receptive field locations throughout the whole field of view. This idea stresses that the neuronal facilitation is spatially global and not
restricted to a local region of focus. A global mechanism could be useful to the visual system because the location of relevent visual items is not always known in advance.
Saenz, Buracas, & Boynton (2002) Global effects of feature-based attention in human visual cortex. Nature Neuroscience. [pdf]
Saenz, Buracas & Boynton (2003) Global feature-based attention for motion and color. Vision Research. [pdf]
How the human brain responds to seeing motion
A movie demo of functional MRI responses.
last updated 8/5/08