1. Department of Psychology University of Washington
Using Pattern Classification Methods to Study the Representation of Stimulus Features in the Human Visual System
Geoffrey M. Boynton
Department of Psychology
University of Washington

2. Our lab is interested in how the neuronal response to a stimulus is affected attention.
It is possible to direct attention to specific features, such as a direction of motion or a color.
Electrophysiological studies in the macaque shows that attention to a particular feature increases the gain of sensory neurons tuned to that feature.

3. Human Area MT+ responds strongly to motion
But the overall BOLD signal will not vary with the direction of motion.

4. However, there are subtle differences in the pattern of responses across voxels that carries useful information about the feature of the stimulus.
Multi-voxel pattern classification algorithms use measures of similarity between patterns of responses across voxels.
Responses across voxels to training stimuli
Response to
test stimulus
Typically, ‘classification accuracy’ is reported, which is the proportion of times that responses to a ‘test’ stimulus most closely matches the response to the correct ‘training’ stimulus.

5. Our Experimental Design
Blank: 6s
Task: Detect brief slowing of attended dots
Stimulus: 14s
Serences and Boynton, Neuron (2007)

6. Serences and Boynton, Neuron (2007)
Classification accuracy, based on response to the attended stimulus.
Replicates Kamitani & Tong,
Current Biology (2006)
MT+
Replicates Kamitani and tong, 2005
Serences and Boynton, Neuron (2007)

7. Serences and Boynton, Neuron (2007)
Classification accuracy, based on response to the unstimulated region of the visual field.
MT+
Serences and Boynton, Neuron (2007)

8. Conclusions
Multi-voxel pattern classification methods allow for the investigation of physiological structures that are organized at a relatively small spatial scale.
These methods are particularly useful for studying the representation of visual features such as orientation, motion or color.
We used these methods to show that attention to a particular direction of motion enhances the responses of all neurons selective to that direction of motion, even in the absence of direct stimulation.