Dissociating the Effect of Noise on Sensory Processing and Overall Decision Difficulty

Abstract

It has been proposed that perceptual decision making involves a task-difficulty component, which detects perceptual uncertainty and guides allocation of attentional resources. It is thought to take place immediately after the early extraction of sensory information and is specifically reflected in a positive component of the event related potentials, peaking at ϳ220 ms after stimulus onset. However, in the previous research, neural processes associated with the monitoring of overall task difficulty were confounded by those associated with the increased sensory processing demands as a result of adding noise to the stimuli. Here we dissociated the effect of phase noise on sensory processing and overall decision difficulty using a face gender categorization task. Task difficulty was manipulated either by adding noise to the stimuli or by adjusting the female/male characteristics of the face images. We found that it is the presence of noise and not the increased overall task difficulty that affects the electrophysiological responses in the first 300 ms following stimulus onset in humans. Furthermore, we also showed that processing of phase-randomized as compared to intact faces is associated with increased fMRI responses in the lateral occipital cortex. These results revealed that noise-induced modulation of the early electrophysiological responses reflects increased visual cortical processing demands and thus failed to provide support for a task-difficulty component taking place between the early sensory processing and the later sensory accumulation stages of perceptual decision making.

Cortical representations of confidence in a visual perceptual decision

“…9a-c). Moreover, by keeping the signal-to-noise ratio constant (Figs 6b and 9b) we illustrated that the certainty correlates were not confounded by a task-difficulty component or noise-induced modulation of sensory processing demands 24 . Both experiments, however, revealed an electrophysiological correlate of decision confidence during the time interval leading from the postcue in Experiment 1 or action cue in Experiment 2, respectively, to the motor response.…”

Sensitivity of event-related brain potentials to task rules

“…Although previous studies had usually changed the level of stimulus saliency to control task difficulty (e.g., Philiastides & Sajda, 2006), a recent study by Bankó et al (2011) showed that this approach can increase the length of sensory neural processes. Consequently, in the previous studies, part of the variation in late ERP components could be due to extended sensory processing for noisier stimuli.…”

“…These studies have shown that the amplitudes of ERPs usually evoked around 300 ms after stimulus onset show a strong correlation to response accuracy, while this correlation is weaker, and usually nonsignificant, for earlier components (Bankó et al, 2011;Philiastides & Sajda, 2006). The other major difference between the neural processes underlying perception and decision-making is that, while the mechanism of object perception can be "category specific" and can vary from one object category to another, decisionmaking processes seem to be "domain general" and act independently of object categories and/or response mechanisms (Heekeren et al, 2006;Heekeren et al, 2008;Ho et al, 2009).…”

“…Recent neuroimaging studies have suggested that a domain-general mechanism of decision-making can be responsible for gathering and comparing sensory information and selecting the proper action, independent of the domain of the sensory input and the type of motor output (Heekeren, Marrett, Bandettini, & Ungerleider, 2004;Heekeren, Marrett, Ruff, Bandettini, & Ungerleider, 2006;Ho, Brown, & Serences, 2009;Kayser, Buchsbaum, Erickson, & D'Esposito, 2010). In parallel, studies of event-related potentials (ERPs) have shown that the neural processes underlying decision-making are linked to the late ERP, usually evoked around 300 ms after stimulus presentation within fronto-parietal electrode sites (Bankó, Gál, Körtvélyes, Kovács, & Vidnyánszky, 2011;Philiastides & Sajda, 2006).…”

“…To detect those processes that can be influenced by decision-making processes, previous studies have searched for ERP components whose variations in amplitude (or timing) are correlated to the level of task difficulty and/or to response accuracy (e.g., Bankó et al, 2011;Philiastides & Sajda, 2006). These studies have shown that the amplitudes of ERPs usually evoked around 300 ms after stimulus onset show a strong correlation to response accuracy, while this correlation is weaker, and usually nonsignificant, for earlier components (Bankó et al, 2011;Philiastides & Sajda, 2006).…”