Task- and Experience-dependent Cortical Selectivity to Features Informative for Categorization

Abstract

In this study, we bridge the gap between monkey electrophysiological recordings that showed selective responses to informative features and human fMRI data that demonstrated increased and selective responses to trained objects. Human participants trained with computer-generated fish stimuli. For each participant, two features of the fish were informative for category membership and two features were uninformative. After training, participants showed higher perceptual sensitivity to the informative dimensions. An fMRI adaptation paradigm revealed that during categorization the right inferior frontal gyrus and occipitotemporal cortex were selectively responsive to the informative features. These selective cortical responses were experience dependent; they were not present for the entire trained object, but specific for those features that were informative for categorization. Responses in the inferior frontal gyrus showed category selectivity. Moreover, selectivity to the informative features correlated with performance on the categorization task during scanning. This all suggests that the frontal cortex is involved in actively categorizing objects and that it uses informative features to do so while ignoring those features that do not contribute category information. Occipitotemporal cortex also showed selectivity to the informative features during the categorization task. Interestingly, this area showed a positive correlation of performance during training and selectivity to the informative features and a negative correlation with selectivity to the uninformative features. This indicates that training enhanced sensitivity to trained items and decreased sensitivity to uninformative features. The absence of sensitivity for informative features during a color change detection task indicates that there is a strong component of task-related processing of these features.

Incremental learning of perceptual and conceptual representations and the puzzle of neural repetition suppression

“…In contrast to these studies, two more recent category learning experiments in humans have found evidence of tuning changes to task-relevant dimensions in the occipitotemporal cortex using fMRI-adaptation (Folstein et al, 2013;van der Linden et al, 2014), as well as strong tuning to category in the prefrontal cortex (van der Linden et al, 2014). The basis of the contrasting results is not entirely clear, but it is possible that the composite nature of the form changes in earlier studies made it more difficult for participants to attend to single relevant form dimensions which could have aided earlier occipitotemporal plasticity.…”

“…Repetition suppression shares many of the empirical characteristics of repetition priming: it is relatively automatic, even occurring in animals under anesthesia (e.g., Miller, Gochin, & Gross, 1991); it can be long-lasting following a small number of stimulus exposures (up to several days, e.g., van Turennout et al, 2000van Turennout et al, , 2003, although effects are strongest with little or no delay (e.g., Grill-Spector & Malach, 2001;Jiang et al, 2000;van Turennout et al, 2003); it is robust to small changes in stimulus form and/or task, with the largest effects when stimuli and tasks are identical across repetition (e.g., Horner & Henson, 2008;Koutstaal et al, 2001;Lueschow, Miller, & Desimone, 1994). Repetition suppression in humans is typically observed throughout the neocortex within regions that are engaged by the task being performed (see Schacter & Buckner, 1998;Wiggs & Martin, 1998, for reviews).…”

“…Consistent with these models, category training studies have yielded evidence that manipulating feature relevance has an impact on learned representations in prefrontal cortex, with cells showing strong preferences for the trained category boundaries. While early studies failed to find much evidence of category tuning in accord with task demands in occipitotemporal regions (e.g., Gillebert et al, 2009;Jiang et al, 2007;Op de Beeck et al, 2001), more recent evidence suggests that these kinds of effects can be observed -albeit at smaller magnitudes than observed in prefrontal cortex (e.g., De Baene et al, 2008;Folstein et al, 2013;van der Linden et al, 2014). Additionally, a number of studies have now documented increases in stimulus selectivity in ventral temporal cortex after extensive training, both in monkeys and in humans (e.g., Baker et al, 2002;Freedman et al, 2006;Jiang et al, 2007;Gillebert et al, 2009; see also Rainer & Miller, 2000).…”

“…Rather than training subjects to categorize novel objects, we had subjects repeatedly name a large set of well-known objects (e.g., dog, hammer, etc.) as is commonly done in studies of repetition priming and repetition suppression (e.g., Cave, 1997;van Turennout et al, 2000van Turennout et al, , 2003. The pressure in this task is quite different to categorization tasks in that the focus is not on the features that are common to objects in the same category but on the distinctive features that are selectively associated with each object's identity and name.…”

“…This is not a small issue for the interpretation of repetition priming and repetition suppression effects over these durations given that these are the intervals over which such effects are largest in magnitude, gradually decaying or suffering from interference over longer intervals (e.g., Li et al, 1993;McKone, 1998;van Turennout et al, 2000van Turennout et al, , 2003. One might also expect that these contexts would have more ecological validity, since they are more in line with what people typically encounter when interacting with objects intermittently in the environment or with their corresponding names in print.…”