Stimulus-driven Effects Research Articles

Influence of emotional expression on the processing of gaze direction

Research demonstrates an influence of gaze direction in emotion recognition. Here we examined whether facial affect similarly influences recognition of gaze direction. Across two studies we found that averted relative to direct gaze was processed more quickly and accurately when coupled with fear, and direct relative to averted gaze with anger. Also evident was that slower overall gaze processing was associated with increased interaction effects between emotion and gaze. Examining individual differences, therefore, enabled us to extend previous research examining speed of processing as a moderator of the interaction effect, while holding constant task demands and stimulus features. Unexpectedly, a main effect emerged such that averted relative to direct gaze was found to be processed more quickly and accurately overall. This effect was not moderated by processing speed and is discussed as a potential stimulus-driven effect that may help explain discrepant findings in the literature.

A cerebral network model of speech prosody comprehension

Comprehension of information conveyed by the tone of voice is highly important for successful social interactions (Grandjean et al., 2006). Based on lesion data, a superiority of the right hemisphere for cerebral processing of speech prosody has been assumed. According to an early neuroanatomical model, prosodic information is encoded within distinct right-sided perisylvian regions which are organized in complete analogy to the left-sided language areas (Ross, 1981). While the majority of lesion studies are in line with the assumption that the right temporal cortex is highly important for the comprehension of speech melody (Adolphs et al., 2001; Borod et al., 2002; Heilman et al., 1984), some studies indicate a widespread network of partially bilateral cerebral regions to contribute to prosody processing including the frontal cortex (Adolphs et al., 2002; Hornak et al., 2003; Rolls, 1999) and the basal ganglia (Cancellieve & Kertesz, 1990; Pell & Leonard, 2003). More recently, functional imaging experiments have helped to differentiate specific functions of distinct brain areas contributing to recognition of speech prosody (Ackermann et al., 2004; Schirmer & Kotz, 2006; Wildgruber et al., 2006). Observations in healthy subjects indicate a strong association of cerebral responses and acoustic voice properties in some regions (stimulus-driven effects), whereas other areas show modulation of activation linked to the focusing of attention to specific task components (task-dependent effects). Here we present a refined model of prosody processing and cross-modal integration of emotional signals from face and voice which differentiates successive steps of cerebral processing involving auditory analysis and multimodal integration of communicative signals within the temporal cortex and evaluative judgements within the frontal lobes.

Cross-modal deactivations during modality-specific selective attention

BackgroundProcessing stimuli in one sensory modality is known to result in suppression of other sensory-specific cortices. Additionally, behavioral experiments suggest that the primary consequence of paying attention to a specific sensory modality is poorer task performance in the unattended sensory modality. This study was designed to determine how focusing attention on the auditory or visual modality impacts neural activity in cortical regions responsible for processing stimuli in the unattended modality.MethodsFunctional MRI data were collected in 15 participants who completed a cued detection paradigm. This task allowed us to assess the effects of modality-specific attention both during the presence and the absence of targets in the attended modality.ResultsThe results of this experiment demonstrate that attention to a single sensory modality can result in decreased activity in cortical regions that process information from an unattended sensory modality (cross-modal deactivations). The effects of attention are likely additive with stimulus-driven effects with the largest deactivations being observed during modality-specific selective attention, in the presence of a stimulus in that modality.ConclusionModality-specific selective attention results in behavioral decrements in unattended sensory modalities. The imaging results presented here provide a neural signature (cross-modal deactivation) for modality-specific selective attention.

Scan patterns during the processing of facial expression versus identity: An exploration of task-driven and stimulus-driven effects

Perceptual studies suggest that processing facial identity emphasizes upper-face information, whereas processing expressions of anger or happiness emphasizes the lower-face. The two goals of the present study were to determine (a) if the distributions of eye fixations reflect these upper/lower-face biases, and (b) whether this bias is task- or stimulus-driven. We presented a target face followed by a probe pair of morphed faces, neither of which was identical to the target. Subjects judged which of the pair was more similar to the target face while eye movements were recorded. In Experiment 1 the probe pair always differed from each other in both identity and expression on each trial. In one block subjects judged which probe face was more similar to the target face in identity, and in a second block subjects judged which probe face was more similar to the target face in expression. In Experiment 2 the two probe faces differed in either expression or identity, but not both. Subjects were not informed which dimension differed, but simply asked to judge which probe face was more similar to the target face. We found that subjects scanned the upper-face more than the lower-face during the identity task but the lower-face more than the upper-face during the expression task in Experiment 1 (task-driven effects), with significantly less variation in bias in Experiment 2 (stimulus-driven effects). We conclude that fixations correlate with regional variations of diagnostic information in different processing tasks, but that these reflect top-down task-driven guidance of information acquisition more than stimulus-driven effects.

Stimulus‐driven and strategic neural responses to fearful and happy facial expressions in humans

The human amygdala responds selectively to consciously and unconsciously perceived facial expressions, particularly those that convey potential threat such as fear and anger. In many social situations, multiple faces with varying expressions confront observers yet little is known about the neural mechanisms involved in encoding several faces simultaneously. Here we used event-related fMRI to measure neural activity in pre-defined regions of interest as participants searched multi-face arrays for a designated target expression (fearful or happy). We conducted separate analyses to examine activations associated with each of the four multi-face arrays independent of target expression (stimulus-driven effects), and activations arising from the search for each of the target expressions, independent of the display type (strategic effects). Comparisons across display types, reflecting stimulus-driven influences on visual search, revealed activity in the amygdala and superior temporal sulcus (STS). By contrast, strategic demands of the task did not modulate activity in either the amygdala or STS. These results imply an interactive threat-detection system involving several neural regions. Crucially, activity in the amygdala increased significantly when participants correctly detected the target expression, compared with trials in which the identical target was missed, suggesting that the amygdala has a limited capacity for extracting affective facial expressions.

A new dichotic listening paradigm in schizophrenia: relationship to focused attentional functioning

Background Classical dichotic listening is a method for studying auditory laterality and consequently basic sensory processing. Nevertheless, by adding instructions about which ear to attend (forced condition), it is possible to also test controlled information processing. Specifically, the forcedright condition would reflect the capacity to focus attention, while the forced-left condition can be explained additionally as a result of inhibitory control over a stimulus-driven effect, since the latter paradigm also involves response conflict. The purpose of the present study was to examine the relationship between the two forced conditions and a test of sustained and focused attention.

On How to Be Unpredictable

The voluntary task-switching paradigm requires subjects to select randomly between tasks and promises to provide a window into executive task selection independent of exogenous influences present in standard task-switching situations. We show here that the degree to which subjects perseverate on tasks across trials captures unique individual differences variance, but also that the switch rate is under strong stimulus-driven control: "Voluntary" switches are much more frequent when the stimulus changes than when it repeats. Most important, we show that individuals whose no-switch trials are selectively slowed exhibit less perseveration and stimulus-driven effects (and thus more voluntary selection) than individuals whose no-switch trials do not show this slowing. We suggest that selective slowing indicates a strategy of treating trials as discrete events--possibly through inhibition of the preceding task set. These results not only demonstrate massive nonvoluntary influences on voluntary selection that are largely untapped by standard task-switching measures, but also show how such influences can be counteracted through strategic adaptations.

Visibility Reflects Dynamic Changes of Effective Connectivity between V1 and Fusiform Cortex

Identifying the neural basis of visibility is central to understanding conscious visual perception. Visibility of basic features such as brightness is often thought to reflect activity in just early visual cortex. But here we show under metacontrast masking that fMRI activity in stimulus-driven areas of early visual cortex did not reflect parametric changes in the visibility of a brightness stimulus. The psychometric visibility function was instead correlated with activity in later visual regions plus parieto-frontal areas, and surprisingly, in representations of the unstimulated stimulus surround for primary visual cortex. Critically, decreased stimulus visibility was associated with a regionally-specific decoupling between early visual cortex and higher visual areas. This provides evidence that dynamic changes in effective connectivity can closely reflect visual perception.

Age-related effects of attentional and oculomotor capture by onsets and color singletons as a function of experience

The present experiment examined the degree to which experience with different stimulus characteristics affects attentional capture, particularly as related to aging. Participants were presented with onset target/color singleton distractor or color singleton target/onset distractor pairs across three experimental sessions. The target/distractor pairs were reversed in the second session such that the target in the first session became the distractor in the second and third sessions. For both young and old adults previous experience with color as a target defining feature influenced oculomotor capture with task-irrelevant color distractors. Experience with sudden onsets had the same effect for younger and older adults, although capture effects were substantially larger for onset than for color distractors. Experience-based capture effects diminished relatively rapidly after target and distractor-defining properties were reversed. The results are discussed in terms of top-down and stimulus-driven effects on age-related differences in attentional control.