Inhibitory control such as active selective response inhibition is currently a major topic in cognitive neuroscience. Here we analyze the shape of behavioral RT and accuracy distributions in a visual masked priming paradigm. We employ discrete time hazard functions of response occurrence and conditional accuracy functions to study what causes the negative compatibility effect (NCE)—faster responses and less errors in inconsistent than in consistent prime target conditions—during the time course of a trial. Experiment 1 compares different mask types to find out whether response-relevant mask features are necessary for the NCE. After ruling out this explanation, Experiment 2 manipulates prime mask and mask target intervals to find out whether the NCE is time-locked to the prime or to the mask. We find that (a) response conflicts in inconsistent prime target conditions are locked to target onset, (b) positive priming effects are locked to prime onset whereas the NCE is locked to mask onset, (c) active response inhibition is selective for the primed response, and (d) the type of mask has only modulating effects. We conclude that the NCE is neither caused by automatic self-inhibition of the primed response due to backward masking nor by updating response-relevant features of the mask, but by active mask-triggered selective inhibition of the primed response. We discuss our results in light of a recent computational model of the role of the BG in response gating and executive control.

Previous studies have argued that faces and other objects are encoded in terms of their deviation from a class prototype or norm. This prototype is associated with a smaller neural population response compared with nonprototype objects. However, it is still unclear (1) whether a norm-based representation can emerge for unfamiliar or novel object classes through visual experience at the time scale of an experiment and (2) whether the results from previous studies are caused by the prototypicality of a stimulus, by the physical properties of individual stimuli independent from the stimulus distribution, and/or by the trial-to-trial adaptation. Here we show with a combined behavioral and event-related fMRI study in humans that a short amount of visual experience with exemplars from novel object classes determines which stimulus is represented as the norm. Prototypicality effects were observed at the behavioral level by behavioral asymmetries during a stimulus comparison task. The fMRI data revealed that class exemplars closest to the prototypes—the perceived average of each class—were associated with a smaller response in the anterior part of the visual object-selective cortex compared with other class exemplars. By dissociating between the physical characteristics and the prototypicality status of the stimuli and by controlling for trial-to-trial adaptation, we can firmly conclude for the first time that high-level visual areas represent the identity of exemplars using a dynamic, norm-based encoding principle.

There is substantial evidence that object representations in adults are dynamically updated by learning. However, it is not clear to what extent these effects are induced by active processing of visual objects in a particular task context on top of the effects of mere exposure to the same objects. Here we show that the task does matter. We performed an event-related fMRI adaptation study in which we derived neural selectivity from a release of adaptation. We had two training conditions: “categorized objects” were categorized at a subordinate level based on fine shape differences (Which type of fish is this?), whereas “control objects” were seen equally often in a task context requiring no subordinate categorization (Is this a vase or not?). After training, the object-selective cortex was more selective for differences among categorized objects than for differences among control objects. This result indicates that the task context during training modulates the extent to which object selectivity is enhanced as a result of training.