Ross Fulham

Switching between univalent task-sets in schizophrenia: ERP evidence of an anticipatory task-set reconfiguration deficit

OBJECTIVE The present study used behavioral and event-related potential (ERP) indices of task-switching to examine whether schizophrenia patients have a specific deficit in anticipatory task-set reconfiguration. METHODS Participants switched between univalent tasks in an alternating runs paradigms with blocked response-stimulus interval (RSI) manipulation (150, 300, 600, and 1200ms). Nineteen high functioning people with schizophrenia were compared to controls that were matched for age, gender, education and premorbid IQ estimate. RESULTS Schizophrenia patients had overall increased RT, but no increase in corrected RT switch cost. In the schizophrenia group, ERPs showed reduced activation of the differential positivity in anticipation of switch trial at the optimal 600ms RSI and reduced activation of the frontal post-stimulus switch negativity at both 600 and 1200ms RSI compared to the control group. CONCLUSIONS Despite no behavioral differences in task switching performance, anticipatory and stimulus-triggered ERP indices of task-switching suggest group differences in processing of switch and repeat trials, especially at longer RSI conditions that for control participants provide opportunity for anticipatory activation of task-set reconfiguration processes. SIGNIFICANCE These results are compatible with impaired implementation of endogenously driven processes in schizophrenia and greater reliance on external task cues, especially at long preparation intervals.

Reactive control processes contributing to residual switch cost and mixing cost across the adult lifespan

In task-switching paradigms, performance is better when repeating the same task than when alternating between tasks (switch cost) and when repeating a task alone rather than intermixed with another task (mixing cost). These costs remain even after extensive practice and when task cues enable advanced preparation (residual costs). Moreover, residual reaction time mixing cost has been consistently shown to increase with age. Residual switch and mixing costs modulate the amplitude of the stimulus-locked P3b. This mixing effect is disproportionately larger in older adults who also prepare more for and respond more cautiously on these “mixed” repeat trials (Karayanidis et al., 2011). In this paper, we analyze stimulus-locked and response-locked P3 and lateralized readiness potentials to identify whether residual switch and mixing cost arise from the need to control interference at the level of stimulus processing or response processing. Residual mixing cost was associated with control of stimulus-level interference, whereas residual switch cost was also associated with a delay in response selection. In older adults, the disproportionate increase in mixing cost was associated with greater interference at the level of decision-response mapping and response programming for repeat trials in mixed-task blocks. These findings suggest that older adults strategically recruit greater proactive and reactive control to overcome increased susceptibility to post-stimulus interference. This interpretation is consistent with recruitment of compensatory strategies to compensate for reduced repetition benefit rather than an overall decline on cognitive flexibility.

Effect of temporal predictability on exogenous attentional modulation of feedforward processing in the striate cortex

Non-informative peripheral visual cues facilitate extrastriate processing of targets [as indexed by enhanced amplitude of contralateral P1 event-related potential (ERP) component] presented at the cued location as opposed to those presented at uncued locations, at short cue-target stimulus onset asynchrony (SOA). Recently, two lines of research are emerging to suggest that the locus of attentional modulation is flexible and depends on 1) perceptual load and 2) temporal predictability of visual stimuli. We aimed to examine the effect of temporal predictability on attentional modulation of feed-forward activation of the striate cortex (as indexed by the C1 ERP component) by high-perceptual-load (HPL) stimuli. We conducted two ERP experiments where exogenously-cued HPL targets were presented under two temporal predictability conditions. In Experiment 1 [high-temporal-predictability (HTP) condition], 17 healthy subjects (age 18-26years) performed a line-orientation discrimination task on HPL targets presented in the periphery of the left upper or diagonally opposite right lower visual field, validly or invalidly cued by peripheral cues. SOA was fixed at 160ms. In Experiment 2 [low-temporal-predictability (LTP) condition], (n=10, age 19-36years) we retained HPL stimuli but randomly intermixed short-SOA trials with long-SOA (1000ms) trials in the task-blocks. In Experiment 1 and the short-SOA condition of the Experiment 2, validly-cued targets elicited significantly faster reaction times and larger contralateral P1, consistent with previous literature. A significant attentional enhancement of C1 amplitude was also observed in the HTP, but not LTP condition. The findings suggest that exogenous visual attention can facilitate the earliest stage of cortical processing under HTP conditions.

Functional brain imaging of auditory prepulse inhibition.

280 this study was to use functional magnetic resonance imaging (fMRI) to identify the neural circuits underlying disturbances processing oddball stimuli in fi rstepisode schizophrenia (FES). Method: fMRI data were collected from 24 people with FES (within 3 months of service contact) and 24 matched healthy controls while performing an auditory oddball task comprising 15% target (high) tones and 85% standard (low) tones. Data were analyzed in SPM2, with event-related analysis of the supramarginal gyrus, thalamus, and limbic and prefrontal cortical areas. Results: The FES group showed signifi cantly reduced activity in the thalamus, hippocampus, dorsal lateral prefrontal cortex and supramarginal gyrus, but a pattern of enhancement as well as reduction in medial prefrontal/anterior cingulate activity, compared with controls. Conclusions: These fi ndings suggest that schizophrenia is associated with impairments in networks for processing salience as well as context from the fi rst episode of this illness. Dysregulation of medial prefrontal areas may refl ect an attempt to compensate for a fundamental breakdown in the coordination of these processes.