Abstract
The link between object perception and neural activity in visual cortical areas is a problem of fundamental importance in neuroscience. Here we show that electrical potentials from the ventral temporal cortical surface in humans contain sufficient information for spontaneous and near-instantaneous identification of a subject’s perceptual state. Electrocorticographic (ECoG) arrays were placed on the subtemporal cortical surface of seven epilepsy patients. Grayscale images of faces and houses were displayed rapidly in random sequence. We developed a template projection approach to decode the continuous ECoG data stream spontaneously, predicting the occurrence, timing and type of visual stimulus. In this setting, we evaluated the independent and joint use of two well-studied features of brain signals, broadband changes in the frequency power spectrum of the potential and deflections in the raw potential trace (event-related potential; ERP). Our ability to predict both the timing of stimulus onset and the type of image was best when we used a combination of both the broadband response and ERP, suggesting that they capture different and complementary aspects of the subject’s perceptual state. Specifically, we were able to predict the timing and type of 96% of all stimuli, with less than 5% false positive rate and a ~20ms error in timing.
Highlights
IntroductionHow does a two-dimensional pattern of pixels measured by our retina get transformed into the percept of a friend’s face or a famous landmark? It is known that the ventral temporal cortex represents different classes of complex visual stimuli within distinct regions
We describe a new technique for decoding perception from electrical potentials measured from the human brain surface
We developed a novel template-projection method for analyzing the electrical potentials, where, for the first time, broadband spectral changes and raw potential changes could be contrasted as well as combined
Summary
How does a two-dimensional pattern of pixels measured by our retina get transformed into the percept of a friend’s face or a famous landmark? It is known that the ventral temporal cortex represents different classes of complex visual stimuli within distinct regions. The ERP and broadband signals show distinct, and partially overlapping, responses to faces [13,19] (Fig 1), but it is unclear whether the information content is itself distinct between the two. While both the ERP and the raw ECoG potential have previously been used to classify object categories [20,21,22], these studies required knowledge about the time of stimulus onset, rather than determining them spontaneously. The ability of the algorithms to establish object category from neural data was well below that of human performance (both in terms of accuracy and temporal fidelity)
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