2013年10月20日日曜日

Prior Expectations Bias Sensory Representations in Visual Cortex

Peter Kok, Gijs Joost Brouwer, Marcel A.J. van Gerven, and Floris P. de Lange
J. Neurosci. 2013;33 16275-16284

ヒトfMRI。
ヒトや動物が物事を「知覚」する時、「実際の感覚情報(例:視覚刺激)」と「事前の知識」を統合していることが知られている。
その統合は、脳内の知覚プロセスの初期(例:視覚野)で行われているのか?
それとも、もっと高次な処理を司る脳部位で行われているのか?
→視覚野の活動が「事前知識」にモジュレートされていた。つまり、感覚情報と事前知識の統合は知覚プロセスの初期段階で行われている。

Perception is strongly influenced by expectations. Accordingly, perception has sometimes been cast as a process of inference, whereby sensory inputs are combined with prior knowledge. However, despite a wealth of behavioral literature supporting an account of perception as probabilistic inference, the neural mechanisms underlying this process remain largely unknown. One important question is whether top-down expectation biases stimulus representations in early sensory cortex, i.e., whether the integration of prior knowledge and bottom-up inputs is already observable at the earliest levels of sensory processing. Alternatively, early sensory processing may be unaffected by top-down expectations, and integration of prior knowledge and bottom-up input may take place in downstream association areas that are proposed to be involved in perceptual decision-making. Here, we implicitly manipulated human subjects' prior expectations about visual motion stimuli, and probed the effects on both perception and sensory representations in visual cortex. To this end, we measured neural activity noninvasively using functional magnetic resonance imaging, and applied a forward modeling approach to reconstruct the motion direction of the perceived stimuli from the signal in visual cortex. Our results show that top-down expectations bias representations in visual cortex, demonstrating that the integration of prior information and sensory input is reflected at the earliest stages of sensory processing.

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