fMRI reveals that involuntary visual deviance processing is resource limited.

Previous studies suggest that involuntary auditory attention evoked by unattended auditory stimuli is not influenced by the primary focus of attention. However, prior studies from our laboratory have found that processing of unattended auditory deviant tones in the auditory and frontal regions is modulated by top-down attentional demands and resource availability. Whether processing of unattended visual deviant stimuli is altered by the availability of attentional resources has not been established. The goal of the current study was to examine the automaticity of these activations, their modulation by attentional capacity, and the neuroanatomical distribution of any attentional effects upon visual deviance detection. We designed an event-related functional magnetic resonance imaging (fMRI) study during which subjects performed a continuous perceptual-motor-visual tracking task whose difficulty was modulated by changing the control dynamics of a joystick. Changes in the anatomical localization, spatial distribution, and intensity of the blood oxygenation level-dependent (BOLD) response associated with unattended infrequent visual changes were examined during low- and high-difficulty tracking conditions of the primary visual task. Results revealed that the unattended deviants elicited BOLD activation in the visual, fusiform, and parietal regions. In these regions, the intensity and extent of the activation evoked by the deviants decreased as a function of the demands of the primary visual task. These findings suggest that processing of unattended visual deviant stimuli is restricted by the attentional demands of a primary task, as previously demonstrated for unattended auditory deviant tones.