Saccadic eye movements are deployed faster for salient facial stimuli, but are relatively indifferent to their emotional content

The present study explores the threat bias for fearful facial expressions using saccadic latency as the response mode, with a particular focus on the role of low-level facial information, including spatial frequency, physical contrast, and apparent, perceived contrast. In a simple localisation task, participants were presented with spatially-filtered versions of neutral, fearful, angry and happy faces. Faces were either composed of naturally-occurring, expression-related differences in contrast, normalised for RMS contrast, or normalised for their apparent, perceived contrast. Together, findings show that saccadic responses are not biased toward fearful expressions compared to neutral, angry or happy counterparts, regardless of their spatial frequency content. Saccadic response times are, however, significantly influenced by the physical contrast of facial stimuli, and the extent to which these are preserved or normalised at the physical (RMS matched) and psychophysical (perceptually matched) level. We discuss the implications of findings for the threat bias literature, and the extent to which image processing can be expected to influence behavioural responses to socially-relevant facial stimuli.

Severe violations of independence in response inhibition tasks

The stop-signal paradigm, a primary experimental paradigm for understanding cognitive control and response inhibition, rests upon the theoretical foundation of race models, which assume that a go process races independently against a stop process that occurs after a stop-signal delay (SSD). We show that severe violations of this independence assumption at short SSDs occur systematically across a wide range of conditions, including fast and slow reaction times, auditory and visual stop signals, manual and saccadic responses, and especially in selective stopping. We also reanalyze existing data and show that conclusions can change when short SSDs are excluded. Last, we suggest experimental and analysis techniques to address this violation, and propose adjustments to extant models to accommodate this finding.

Dynamic shifts of visual and saccadic signals in prefrontal cortical regions 8Ar and FEF

A central question in neuroscience is how the brain transitions from sensory representations to motor outputs. The prefrontal cortex contains neurons that have long been implicated as important in this transition and in working memory. We found evidence for rich and diverse tuning in these neurons, which was often spatially misaligned between visual and saccadic responses. This feature may play an important role in flexible working memory capabilities.

Severe violations of independence in response inhibition tasks

The stop-signal paradigm, a primary experimental paradigm for understanding cognitive control and response inhibition, rests upon the theoretical foundation of race models, which assume that a go process races independently against a stop process that occurs after a stop-signal delay (SSD). We show that severe violations of this independence assumption at short SSDs occur systematically across a wide range of conditions, including fast and slow RTs, auditory and visual stop signals, manual and saccadic responses, and especially in selective stopping. We also reanalyze existing data and show that conclusions can change when short SSDs are excluded. Finally, we suggest experimental and analysis techniques to address this violation, and propose adjustments to extant models to accommodate this finding.

Sensory adaptation and inhibition of return: Dissociating multiple inhibitory cueing effects

Inhibition of return (IOR) refers to an increase in reaction times to targets that appeared at a previously cued location relative to an uncued location, often investigated using a spatial cueing paradigm. Despite numerous studies that have examined many aspects of IOR, the neurophysiological mechanisms underlying IOR are still in dispute. The objective of the current research is to investigate the plausible mechanisms by manipulating the cue and target types between central and peripheral stimuli in a traditional cue-target paradigm with saccadic responses to targets. In peripheral cueing conditions, we observed inhibitory cueing effects across all cue-target onset asynchronies (CTOAs) with peripheral targets, but IOR was smaller and arose later with central targets. No inhibition was observed in central cueing conditions at any CTOAs. Empirical data were simulated using a two-dimensional dynamic neural field model. Our results and simulations support previous work demonstrating that, at short CTOAs, behavioral inhibition is only observed with repeated stimulation – an effect of sensory adaptation. With longer CTOAs, IOR is observed regardless of target type, when peripheral cueing is used. Our findings suggest that behaviorally exhibited inhibitory cueing effects can be attributed to multiple mechanisms, including both attenuation of visual stimulation and local inhibition in the superior colliculus.