Talks and Conference Presentations
Cognitive Neuroscience Society
11th Annual Meeting
April 18-20, 2004
San Francisco, California
Spatial Specificity of Impoverished Face and Object Stimuli in the Fusiform Gyrus
Lisa H. Berghorst1,6, Scott A. Huettel1,2,3,4, & Gregory McCarthy1,3,4,5
Previous electrophysiological, neuroimaging, and lesion studies have demonstrated that regions within the fusiform gyrus show selective activity to images of faces compared to other stimuli (Kanwisher et al., 1997; McCarthy et. al, 1997). In the present studies, we explore whether greatly impoverished face stimuli evoke activity within these regions and how the processing of impoverished face stimuli is influenced by prior stimulus context.
In Experiment 1, we presented line drawings of faces (Brunswik & Rieter, 1938) and objects while measuring changes in brain activity using fMRI at 4T. We investigated whether such simple faces reliably activated ventral visual regions, whether activity depended upon the orientation of the stimulus, and whether face selective regions showed selectivity for impoverished faces. Previous results have suggested that specificity is greatly reduced to such simple stimuli (Peters et al., 2000).
In Experiment 2, we examined the influence of irrelevant priming information upon behavioral responses to these faces in a simple discrimination task. We evaluated whether processing of these simple faces can be influenced by the characteristics of a priming stimulus, and whether priming effects depended upon the hemisphere of processing.
Content and Function Words Differentiated by Gray and White Matter Activations
Michele T. Diaz1,2 and Gregory McCarthy1,2,3,4
Content and Function words differ in their purpose and semantic content; differential neural bases for such words are supported by previous research (Friederici et al., 2000). We investigated processing of these words using functional Magnetic Resonance Imaging (fMRI). Previous fMRI studies investigating semantic processing involved passive reading, an explicit semantic task, or comparisons across tasks (e.g. Petersen et al., 1990, Binder et al., 1997). While these manipulations involve semantic processing, it is likely that other processes are also involved (e.g. strategic processes, intrusive thoughts, differential attentional demands). In the present experiment, a stream of random letter strings (2/sec) was displayed, to which participants performed a matching task. Incidental to the overt task, open and closed class words were interspersed randomly among nonwords (1/12-15sec). The nonword baseline served as a control condition for orthographic and letter level processing. The task ensured participant engagement while limiting strategic processing of critical stimuli. The stimuli were contrasted to investigate activation to 1) word and nonword processing and 2) levels of semantic processing. An inverse spiral acquisition sequence was utilized for improved recovery of signal from anterior temporal areas, which have been linked to semantic processing through lesion studies. Areas that differentiated word classes were temporal, parahippocampal, and longitudinal fasciculi, with greater content than function word activation. Most novel, were the bilateral longitudinal fasciculi activations, which extended anteriorly, possibly indicating more extensive processing and functional connectivity for content words. Several analyses limit the possibility that these activations were due to artifact.
Scalp-Recorded N170 Is Influenced by the Context of a Perceived Gaze Shift
James P. Morris1,2, Ayelet Landau3, Shlomo Bentin3, and Gregory McCarthy1,2,4
Prior studies from our laboratory established that faces evoke a negative event-related potential (ERP) with a latency of approximately 170 msec (N170) that is focally distributed over the (primarily right) posterior temporal scalp (Bentin et al., 1996). Further studies by Puce et al. (2000) showed that N170 is preferentially evoked by the perception of dynamic gaze shifts that averted from central fixation. Recent neuroimaging evidence has demonstrated that the posterior (primarily right) STS is sensitive to gaze shifts (Puce et al., 1998), and furthermore, that this activity is modulated by context (Pelphrey et al., 2003). In this latter study, the perception of eye gaze shifts that did not properly acquire a visual target evoked longer duration activation than a gaze shift that acquired the target.
By providing a target for the gaze shift, we investigated whether or not contextual factors could influence the N170 and related components elicited by gaze shifts. In this study, subjects viewed an animated face that remained present throughout each experimental run. Each trial consisted of the appearance of a flashing checkerboard target, followed by the animated character making gaze shifts that acquired (correct) or did not acquire (incorrect) the target. With this design, we tested the hypothesis that the N170 and related ERP components would reflect processes sensitive to the intention of perceived gaze shifts.
Grasping the Intentions of Others: The Perceived Intentionality of an Action Influences Activity in the Superior Temporal Sulcus during Social Perception
Kevin A. Pelphrey, James P. Morris, Gregory McCarthy
An explication of the neural substrates for social perception is an important component in the emerging field of social cognitive neuroscience. Prior studies have demonstrated that passive viewing of biological motion (Allison et al., 2000; Puce et al., 1998; Pelphrey et al., 2003a) activates the posterior superior temporal sulcus (STS) region. Furthermore, the perceived context of observed gaze shifts (Pelphrey et al., 2003b, Pelphrey et al., in press) modulates STS activity.
In this study, we investigated brain activity in response to viewing of goal- and non-goal-directed reaching-to-grasp movements. Participants viewed an animated character making reaching-to-grasp movements either toward (correct) or away (incorrect) from a blinking dial. Both conditions evoked significant posterior STS activity that was strongly right lateralized. By examining the time course of the BOLD response from areas of activation, we observed a functional dissociation. Incorrect trials evoked significantly greater activity in the STS than did correct trials, while an area posterior and inferior to the STS (likely corresponding to the MT/V5 complex) responded equally to correct and incorrect movements.
Our results further suggest that a region of the right posterior STS is involved in analyzing the intentions of other people's actions and that activity in this region is sensitive to the context of observed biological motions.
Reward uncertainty and decision uncertainty independently modulate activity in brain systems for decision making
Jonathan K. Smith1, Evan M. Gordon1,5, Richard D. Sheu1,5 and Scott A. Huettel1,2,3,4
Studies of decision making often focus on decision making under uncertainty; that is, when information about the probabilities of different outcomes is limited. Models of decision making under uncertainty posit a dorsal prefrontal-parietal system, with dorsolateral prefrontal cortex (dlPFC) supporting behavioral selection processes and posterior parietal cortex supporting the evaluation of the expected outcome of decision options. However, some decisions are made not under uncertainty but under risk; that is, when the probability of different reward outcomes is known. The processing of the reward consequences of actions has been linked to ventromedial prefrontal cortex (vmPFC), while the selection and control of risky behaviors has been linked to insular cortex.
We used fMRI to investigate the brain systems that support decision making in the presence and absence of uncertainty and risk. On each trial, subjects viewed a single stimulus, executed a response, and received reward feedback. Some of the stimuli were associated with predetermined decisions and/or reward probabilities, while others were not. Subjects were trained on all stimulus-response contingencies before entering the scanner, and behavioral performance was near ceiling.
We hypothesized that, as shown in previous studies, there would be significant decision-phase activity in dlPFC and related brain regions. Likewise, we hypothesized that there would be significant reward-phase activity in vmPFC and related brain regions. Of key interest were the effects of reward information upon decision-related activity. We hypothesized that if decision-irrelevant risk information guides decision-making, activity in dlPFC would increase for risky trials. Furthermore, if the insular cortex supports the control of risky behavior, not only should its activity increase to unexpected absences of reward, but it should be sustained until the subsequent trial.
Effects Of Attentional Load On Mismatch Negativity
Günes Yücel1,3, Christopher M. Petty1,3, Gregory McCarthy1,3, and Aysenil Belger1,2
The auditory mismatch negativity (MMN) response is maximal over the frontocentral scalp, and has been localized to fronto-temporal generator source. While the temporal generators have been associated with the sensory processing of deviant tones, the frontal generators have been linked to signals triggering a shift of attention towards the initially unattended stimuli. This study examined the modulation of fronto-temporal cortical responses elicited by involuntary shift of auditory attention using a dual-task design. Event related potentials (ERPs) were recorded from 31 scalp electrodes in 15 subjects performing a visual tracking task under two levels of complexity, while simultaneously listening to task-irrelevant tones that they were instructed to ignore. Tracking task complexity was modulated by changing the joystick dynamics (i.e. first-order (velocity tracking versus second-order (acceleration) tracking). Auditory stimuli consisted of frequently presented "standard" tones (600 Hz, ~92%) and infrequent, "deviant" tones (780 Hz, ~8%) of 200 ms duration. Changes in MMN amplitude as a function of the complexity of the primary visual task were computed. The results revealed that unattended deviant tones elicited MMN and P3 responses during both visual tracking tasks. Furthermore, the MMN amplitude was greater over fronto-central sites during the first-order tracking task as compared to the second-order tracking task, whereas the MMN amplitudes measured at the temporal sites did not show modulations by tracking task complexity. These results suggest that the complexity of a primary visual task affects involuntary attention to the unattended deviant tones and these attention modulation effects are primarily controlled by frontal regions.