A previous PET study comparing novel versus repeated objects using a blocked stimulus design

Clark, Vincent P., Jose M. Maisog, and James V. Haxby. fMRI designs also makes it difficult to compare the results of these study of face perception and memory using random stimulus sefMRI investigations with those of previous electrophysioquences. J. Neurophysiol. 79: 3257–3265, 1998. A new functional logical and psychophysical research that have used randommagnetic resonance imaging (fMRI) method was used to investiized designs. Furthermore, the specificity of functional data gate the functional neuroanatomy of face perception and memory. obtained using blocked designs may be compromised by Whole-brain fMRI data were acquired while four types of stimuli a number of factors, including the subjects’ expectancies were presented sequentially in an unpredictable pseudorandom orregarding upcoming stimuli within and between blocks, and der at a rate of 0.5 Hz. Stimulus types were a single repeated changes in subjects’ attentional state and level of arousal memorized target face, unrepeated novel faces, nonsense scrambled between blocks. faces, and a blank screen. Random stimulus sequences were designed to generate a functional response to each stimulus type that Most previous attempts to overcome problems associated was uncorrelated with responses to other stimuli. This allowed with blocked stimulus designs have used single trial designs fMRI responses to each stimulus type to be examined separately with slow stimulus presentation rates to reduce the overlap using multiple regression. Signal increases were found for all stimof the hemodynamic response evoked by consecutive trials uli in ventral posterior cortex. Responses to intact faces extended (Boynton et al. 1996; Buckner et al. 1996; McCarthy et al. to more anterior locations of occipitotemporal cortex than did re1997a; Zarahn et al. 1997). This method limits the number sponses to scrambled faces, consistent with previous studies of of trials that may be collected in individual experiments, face perception. Responses evoked by novel faces were in regions and the use of long intervals without stimuli may influence of ventral occipitotemporal cortex medial to regions in which significant responses were evoked by the target face. The repeated subjects’ level of attention and arousal. A recent paper by target face stimulus also evoked activity in widely distributed reDale and Buckner (1997) used stimulus presentation rates gions of frontal and parietal cortex. These results demonstrate that as fast as one stimulus every 2 s and showed that responses cortical hemodynamic responses to interleaved novel and repeated in retinotopically organized lower-order visual cortical areas stimuli can be distinguished and measured using fMRI with approof the right and left hemispheres responded selectively to priate stimulus sequences and data analysis methods. This method stimuli positioned in the left and right visual fields, respeccan now be used to examine the neural systems involved in cognitively. In the present study, we investigated whether differentive tasks that were previously impossible to study using positron tial responses in higher-order visual cortical areas to different emission tomography or fMRI. types of stimuli presented rapidly in the same visual field location can be distinguished using fMRI.