A step toward understanding the human ventral visual pathway

Category-specific and category-general neural codes of recognition memory in the ventral visual pathway

Researchers have identified category-specific brain regions, such as the fusiform face area (FFA) and parahippocampal place area (PPA) in the ventral visual pathway, which respond preferentially to one particular category of visual objects. In addition to their category-specific role in visual object identification and categorization, regions in the ventral visual pathway play critical roles in recognition memory. Nevertheless, it is not clear whether the contributions of those brain regions to recognition memory are category-specific or category-general. To address this question, the present study adopted a subsequent memory paradigm and multivariate pattern analysis (MVPA) to explore category-specific and category-general neural codes of recognition memory in the visual pathway. The results revealed that the right FFA and the bilateral PPA showed category-specific neural patterns supporting recognition memory of faces and scenes, respectively. In contrast, the lateral occipital cortex seemed to carry category-general neural codes of recognition memory. These results provide neuroimaging evidence for category-specific and category-general neural mechanisms of recognition memory in the ventral visual pathway.

Temporal dynamics of the neural representation of hue and luminance polarity

Hue and luminance contrast are basic visual features. Here we use multivariate analyses of magnetoencephalography data to investigate the timing of the neural computations that extract them, and whether they depend on common neural circuits. We show that hue and luminance-contrast polarity can be decoded from MEG data and, with lower accuracy, both features can be decoded across changes in the other feature. These results are consistent with the existence of both common and separable neural mechanisms. The decoding time course is earlier and more temporally precise for luminance polarity than hue, a result that does not depend on task, suggesting that luminance contrast is an updating signal that separates visual events. Meanwhile, cross-temporal generalization is slightly greater for representations of hue compared to luminance polarity, providing a neural correlate of the preeminence of hue in perceptual grouping and memory. Finally, decoding of luminance polarity varies depending on the hues used to obtain training and testing data. The pattern of results is consistent with observations that luminance contrast is mediated by both L-M and S cone sub-cortical mechanisms.

Attention control processes that prioritise task execution may come at the expense of incidental memory encoding

Attention underpins episodic memory encoding by gating information processing. However, it is unclear how different forms of attention affect encoding. Using fMRI, we implemented a novel task that separates top-down and bottom-up attention (TDA; BUA) to test how these forms of attention influence encoding. Twenty-seven subjects carried out a scanned incidental encoding task that required semantic categorisation of stimuli. Trials either required visual search (TDA) to locate a target, or the target blinked and captured attention (BUA). After a retention period, subjects performed a surprise recognition test. Univariate analyses showed that ventral visual regions and right hippocampus indexed encoding success. Psychophysiological interaction analyses showed that, during TDA, there was increased coupling between dorsal parietal cortex and fusiform gyrus with encoding failure, and between lateral occipital cortex and fusiform gyrus with encoding success. No significant connectivity modulations were observed during BUA. We propose that increased TDA to objects in space is mediated by parietal cortex and negatively impacts encoding. Also, increases in connectivity within ventral visual cortex index the integration of stimulus features, promoting encoding. Finally, the influences of attention on encoding likely depend on task demands: as cognitive control increases, task execution is emphasised at the expense of memory encoding.