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Steven Hillyard, PhD

Steven Hillyard, PhD

Professor Emeritus

Contact Information

We are studying the neural bases of perceptual and cognitive processes in humans by means of noninvasive recordings of electrophysiological brain activity in conjunction with other neuroimaging techniques. The overall aim is to identify and characterize spatio-temporal patterns of brain activity that underlie specific information processing stages during perception, selective attention, stimulus recognition, and memory storage and retrieval.

Selective Attention to Features and Objects. Visual stimuli may be selectively attended on the basis of their location in the environment or on the basis of having particular features such as color or shape or combinations of features. In this project, event-related brain potentials (ERPs) are recorded in response to stimuli having specific features that are being attended, and the associated ERP fields are mapped over the scalp. By using source localization algorithms in conjunction with magnetic resonance imaging, the locations of the neural generators of attention-related ERPs can be calculated with respect to brain anatomy. With these techniques we have found that attention to different classes of features produces enhanced neural activity in discrete zones of extrastriate visual cortex of the dorsal and ventral processing streams at specific times after stimulus presentation.

Cross-modal Integration in Spatial Attention. There has been some controversy about whether paying attention to a specific event or object in the environment involves the enhanced processing of all its separate attributes or just those aspects that are relevant at the moment. For example, if both sounds and flashes are presented at a particular location, is it possible to attend to each of these modalities separately, or does attention to location invariably produce a facilitation of all modalities occurring at that location. By recording ERPs to the sounds and flashes, we have found that spatial attention is multi-modal and facilitates even stimuli in non-relevant modalities at an attended location. This attentional mechanism appears to integrate different aspects of a spatially localized event into a unified percept of a multimodal object.

Steady State Visual Evoked Potentials. If a visual stimulus is presented repetitively at a rate of 5-6 Hz or greater, a continuous oscillatory electrical response is elicited in the visual pathways that is termed the steady state visual evoked potential (SSVEP). The SSVEP can be recorded from the scalp as a nearly sinusoidal waveform having the same fundamental frequency as the driving stimulus and often includes higher harmonics. We have found that the amplitude of the SSVEP can be substantially increased when the flickering stimulus is being attended in relation to when it is ignored. Recordings of the SSVEP offer certain advantages over transient ERPs in the study of attention, since the SSVEP signal is continuously available and can be more readily distinguished from background EEG noise. Because the SSVEP yields fine-grained temporal and spatial information about the focusing of visual attention, we are recording SSVEPs to investigate mechanisms of attentional switching from one stimulus to another and attention to multi-dimensional objects in the visual fields.

McDonald, J.J., W.A. Teder-Sälejärvi and S.A. Hillyard. Involuntary orienting to sound improves visual perception. Nature 407: 906-908, 2000.

McDonald, J.J., W.A. Teder-Sälejärvi, F. Di Russo and S.A. Hillyard. Neural substrates of perceptual enhancement by cross-modal spatial attention. Journal of Cognitive Neuroscience 15: 10-19, 2003.

Di Russo, F., A. Martinez and S.A. Hillyard. Source analysis of event-related cortical activity during visuo-spatial attention. Cerebral Cortex 13: 486-499, 2003.

Muller, M.M., P. Malinowski, T. Gruber and S.A. Hillyard. Sustained division of the attentional spotlight. Nature 424: 309-312, 2003.

Schoenfeld, M.A., C. Tempelmann, A. Martinez, J.-M. Hopf, C. Sattler, H.-J. Heinze and S.A. Hillyard. Dynamics of feature binding during object-selective attention. Proceedings of the National Academy of Sciences 100: 11806-11811, 2003.

Hillyard, S.A., F. Di Russo and A. Martinez. The imaging of visual attention. In: N. Kanwisher and J. Duncan (Eds.). Attention and Performance XX: Functional Neuroimaging of Visual Cognition. Oxford Univ. Press, Oxford, 2003, Pp. 379-388.

McDonald, J.J., W.A. Teder-Salejarvi, F. Di Russo and S.A. Hillyard. Neural basis of auditory-induced shifts in visual time-order perception. Nature Neuroscience, July 2005.

Khoe, W., J.F. Mitchell, J.H. Reynolds and S.A. Hillyard. Exogenous attentional selection of transparent superimposed surfaces modulates early event-related potentials. Vision Research 45 (2005), 3004-3014.

M. M. Muller, S. Andersen, N. J. Trujillo, P. Valdes-Sosa, P. Malinowski, and S. A. Hillyard. Feature-selective attention enhances color signals in early visual areas of the human brain. PNAS, 2006; 103: 14200-14205.

Martinez, A., W. Teder-Salejarvi, M. Vazquez, S. Molholm, J.J. Foxe, D.C. Javitt, F. Di Russo, M.S. Worden and S.A. Hillyard. Objects are highlighted by spatial attention. Journal of Cognitive Neuroscience, 2006;18:298-310.

Mishra, J., Martinez, A., Sejnowski, T.J., Hillyard, S.A. Early cross-modal interactions in auditory and visual cortex underlie a sound-induced visual illusion. The Journal of Neuroscience, 27(15):4120-4131, 2007.

Martinez, A., Ramanathan, D.S., Foxe, J.J., Javitt, D.C., Hillyard, S.A. The Role of Spatial Attention in the Selection of Real and Illusory Objects. The Journal of Neuroscience, 27(30):7963-7973, 2007.

Bonath, B., Noesselt, T., Martinez, A., Mishra, J., Schwlecker, K., Heinze, H.J., Hillyard, S.A. Neural Basis of the Ventriloquist Illusion. Current Biology 17, 1697-1703, 2007.

Khoe, W. Mitchell, J.F., Reynolds, J.H., Hillyard, S.A. ERP evidence that surface-based attention biases interocular competition during rivalry. The Journal of Vision, 8(3):18, 1-11, 2008.

Mishra, J., Martinez, A., Hillyard, S.A. Cortical processes underlying sound-induced flash fusion. Brain Research, 1242:102-115, 2008.

Andersen, S.K., Hillyard, S.A., Muller, M.M. Attention Facilitates Multiple Stimulus Features in Parallel in Human Visual Cortex. Current Biology 18, 1006-1009, 2008.

Hagler, D.J., Jr., Halgren, E., Martinez, A., Huang, M., Hillyard, S.A., Dale, A.M. Source estimates for MEG/EEG visual evoked responses constrained by multiple, retinotopically-mapped stimulus locations. Human Brain Mapping, in press.

Mishra, J., Hillyard, S.A. Endogenous attention selection during binocular rivalry at early stages of visual processing. Vision Research, in press.