Rachel Swainson

Feedback-related negativity codes prediction error but not behavioral adjustment during probabilistic reversal learning

We assessed electrophysiological activity over the medial frontal cortex (MFC) during outcome-based behavioral adjustment using a probabilistic reversal learning task. During recording, participants were presented two abstract visual patterns on each trial and had to select the stimulus rewarded on 80% of trials and to avoid the stimulus rewarded on 20% of trials. These contingencies were reversed frequently during the experiment. Previous EEG work has revealed feedback-locked electrophysiological responses over the MFC (feedback-related negativity; FRN), which correlate with the negative prediction error [Holroyd, C. B., & Coles, M. G. The neural basis of human error processing: Reinforcement learning, dopamine, and the error-related negativity. Psychological Review, 109, 679–709, 2002] and which predict outcome-based adjustment of decision values [Cohen, M. X., & Ranganath, C. Reinforcement learning signals predict future decisions. Journal of Neuroscience, 27, 371–378, 2007]. Unlike previous paradigms, our paradigm enabled us to disentangle, on the one hand, mechanisms related to the reward prediction error, derived from reinforcement learning (RL) modeling, and on the other hand, mechanisms related to explicit rule-based adjustment of actual behavior. Our results demonstrate greater FRN amplitudes with greater RL model-derived prediction errors. Conversely expected negative outcomes that preceded rule-based behavioral reversal were not accompanied by an FRN. This pattern contrasted remarkably with that of the P3 amplitude, which was significantly greater for expected negative outcomes that preceded rule-based behavioral reversal than for unexpected negative outcomes that did not precede behavioral reversal. These data suggest that the FRN reflects prediction error and associated RL-based adjustment of decision values, whereas the P3 reflects adjustment of behavior on the basis of explicit rules.

ERP correlates of a receptive language-switching task

Previous research has shown large response time costs (in excess of 50 ms) when bilingual speakers switch predictably back and forth between naming items (a productive switching task) in their first (L1) and second languages (L2). A recent study using event-related potentials (ERPs) has shown that switching between languages is associated with activity over frontal (N2) and parietal (late positive complex) areas of cortex (Jackson, Swainson, Cunnington, & Jackson, 2001). Switching between naming in different languages requires a switch in both language representations and language-specific motor responses. The current study investigated a receptive (input) language-switching task with a common manual response. Number words were presented in L1 and L2, and participants were required to judge whether the words were odd or even (a parity judgement). Response costs were considerably reduced, and the frontal and parietal switch related activity reported in the productive switching task was absent. Receptive switching was associated with early switch-related activity over central sensors that were not language specific. These results are discussed in relation to the idea that there is no language-specific lexical selection mechanism. Instead the costs of receptive language switching may arise from outside the bilingual lexicon.

Behavioural and neurophysiological correlates of bivalent and univalent responses during task switching

A hallmark of human behaviour is its flexibility. In any given circumstance there is typically a range of possible responses that could be selected. In the current study participants were presented with stimulus displays that afforded two simple cognitive tasks and were required to switch predictably between them. The judgements for each task were either uniquely mapped onto separate effectors (univalent conditions) or else mapped onto shared effectors (bivalent condition). The results demonstrated that whilst behavioural switch costs were similar across the mapping conditions, these conditions differed in the patterns of brain activity observed during task preparation and early visual processing of the target. Specifically, a cue-locked switch-related late frontal negativity was present over frontal sensors for the bivalent condition only, and a target-locked N1 over occipital sensors was larger in the bivalent condition than the univalent conditions. In contrast, a switch-related target-locked P3b component was common to all mapping conditions. These findings are discussed with respect to differences in processing demands for switching between tasks with bivalent versus univalent responses.

ERP indices of persisting and current inhibitory control: A study of saccadic task switching

Previous studies have found that inhibition of a biologically dominant prepotent response tendency is required during the execution of a less familiar, non-prepotent response. However, the lasting impact of this inhibition and the cognitive mechanisms to flexibly switch between prepotent and non-prepotent responses are poorly understood. We examined the neurophysiological (ERP) correlates of switching between prosaccade and antisaccade responses in 22 healthy volunteers. The behavioural data showed significant switch costs in terms of response latency for the prosaccade task only. These costs occurred exclusively in trials when preparation for the switch was limited to 300 ms, suggesting that inhibition of the prepotent prosaccade task either passively dissipated or was actively overcome during the longer 1000 ms preparation interval. In the neurophysiological data, a late frontal negativity (LFN) was visible during preparation for a switch to the prosaccade task that was absent when switching to the antisaccade task, which may reflect the overcoming of persisting inhibition. During task implementation both saccade types were associated with a late parietal positivity (LPP) for switch relative to repetition trials, possibly indicating attentional reorienting to the switched-to task, and visible only with short preparation intervals. When the prosaccade and antisaccade task were contrasted directly during task implementation, the antisaccade task exhibited increased stimulus-locked N2 and decreased P3 amplitudes indicative of active inhibition. The present findings indicate that neurophysiological markers of persisting and current inhibition can be revealed using a prosaccade/antisaccade-switching task.

Do women with fragile X syndrome have problems in switching attention: Preliminary findings from ERP and fMRI

Fragile X syndrome (FXS) is a neurodevelopmental disorder that represents the most common known cause of developmental delay. Recent neuropsychological findings indicate that females with FXS present with a specific pattern of cognitive deficits and that these difficulties primarily involve skills requiring executive control. The present study is the first to examine the extent to which neural activity of females with FXS can be observed on a task that specifically taps two core deficits, namely switching and response inhibition. Brain activity was measured using both event-related electrical potentials (ERPs) and event-related functional MRI (fMRI) neuroimaging in separate studies using the same cognitive paradigm. Compared to controls, females with FXS were significantly slower and made more errors on trials that required an immediate response (Go) to stimulus onset but were comparable on trials that required a delayed response (Wait) to stimulus onset. At the brain level, several areas showed significantly greater activation for females with FXS compared with controls, including the cingulate cortex and left and right ventral prefrontal areas. In contrast, no areas were found to show significantly greater activation for controls compared with females with FXS.

Attention, competition, and the parietal lobes: insights from Balint's syndrome.

Simultanagnosia (resulting from occipito-parietal damage) is a profound visual deficit, which impairs the ability to perceive multiple items in a visual display, while preserving the ability to recognise single objects. Here we demonstrate in a patient presenting with Balint’s syndrome that this deficit may result from an extreme form of competition between objects which makes it difficult for attention to be disengaged from an object once it has been selected.

Event related potentials reveal that increasing perceptual load leads to increased responses for target stimuli and decreased responses for irrelevant stimuli

Lavie (1995) have suggested that perceptual processing is influenced by perceptual load. Specifically, relevant information receives additional processing in high load situations exhausting the available capacity. On the other hand, irrelevant information receives less processing with increasing load on a relevant task, as there is a reduced amount of residual processing available. Rees et al. (1997) provided the first physiological evidence for this model, showing this pattern in a functional magnetic resonance imaging study. Likewise, Handy et al. (2001) offered supporting evidence measuring event related potentials (ERPs). Both of these studies presented irrelevant information in peripheral vision. Here we manipulated load while using the identical stimuli and the same task (a peripheral gap judgment task) with centrally presented irrelevant stimuli. ERPs show the pattern predicted by Lavie and colleagues, specifically for the N1 component. This work offers further evidence that visual attention modulates relatively early processing of perceptual information. Specifically, increasing load resulted in stronger N1 responses to relevant information and weaker N1 responses to irrelevant information.

The role of spatial information in advance task-set control: an event-related potential study

Task‐switching has proved to be a fruitful paradigm for studying cognitive control mechanisms. Interestingly, this avenue of study has revealed that subjects are, to some degree, able to bring about a change in task‐set prior to the performance of that task (provided that they are given advance warning of the upcoming task, for instance in the form of a cue). Event‐related potentials (ERPs) have proved to be a good way of measuring these rapid anticipatory control processes. To explore these processes further, the current study examined the relationship between the availability of spatial information and cue‐locked task‐switching ERP effects. Two groups of subjects were compared: one group could separate the task‐sets on the basis of the targets’ colour (the ‘colour’ group), the second on the basis of the targets’ location (the ‘spatial’ group). The performance of both groups benefited to the same extent from advance cueing of task‐transitions (switches or repeats), yet the ERP data revealed cue‐locked (but not target‐locked) differences between the two groups. The most striking of these differences was the absence of both a late positivity over posterior scalp and a late negativity over frontal scalp when the spatial group switched between tasks. Thus, it seems unlikely that these effects index stimulus‐response ‘reconfiguration’per se– as the mappings were identical for both groups of subjects – but rather that these task‐switching processes are sensitive to how the mappings are represented.

Mental Representation of Number in Different Numerical Forms

How are numerical operations implemented within the human brain? It has been suggested that there are at least three different codes for representing number: a verbal code that is used to manipulate number words and perform mental numerical operations (e.g., multiplication), a visual code that is used to decode frequently used visual number forms (e.g., Arabic digits), and an abstract analog code that may be used to represent numerical quantities. Furthermore, each of these codes is associated with a different neural substrate. We extend these studies using dense-sensor event-related EEG recording techniques to investigate the temporal pattern of notation-specific effects observed in a parity judgement (odd versus even) task in which single numbers were presented in one of four different numerical notations. Contrasts between different notations demonstrated clear modulations in the visual evoked potentials (VEP) recorded. We observed increased amplitudes for the P1 and N1 components of the VEP that were specific to Arabic numerals and to dot configurations but differed for random and recognizable (die-face) dot configurations. These results demonstrate clear, notation-specific differences in the time course of numerical information processing and provide electrophysiological support for the triple-code model of numerical representation.

Two measures of task-specific inhibition

Inhibition has been implicated as an important mechanism for task-set control, ensuring the efficient selection of the to-be-performed task over alternative possibilities. Across three experiments we demonstrated the effects of two potentially different types of task inhibition. The first is the inhibition of a task that concurrently affords an incongruent response, which is labelled dimension inhibition (Goschke, 2000). Using targets that afford three tasks, we demonstrated that this only occurs when a single alternative task affords an incongruent response, with the inhibition being specific to that task. The second type of inhibition that we observed was backwards inhibition—the suppression of a recently abandoned task-set (Mayr & Keele, 2000). Unlike dimension inhibition, backwards inhibition was not triggered by the response incongruence of the unperformed tasks, or even whether the target afforded responses via the unperformed tasks. These two purported types of inhibition did not co-occur, and neither did the factors of response congruence and whether that task was recently abandoned interact. We therefore suggest that task-specific inhibition can be applied/triggered differently depending upon the paradigm, perhaps depending upon the extent to which alternative tasks, and therefore potentially other responses, are triggered by the target.