Effects of feature and spatial attention on visual change detection

P3a from white noise

P3a and P3b event-related brain potentials (ERPs) were elicited with an auditory three-stimulus (target, distracter, and standard) discrimination task in which subjects responded only to the target. Distracter stimuli consisted of white noise or novel sounds with stimulus characteristics perceptually matched. Target/standard discrimination difficulty was manipulated by varying target/standard pitch differences to produce relatively easy, medium, and hard tasks. Error rate and response time increased with increases in task difficulty. P3a was larger for the white noise compared to novel sounds, maximum over the central/parietal recording sites, and did not differ in size across difficulty levels. P3b was unaffected by distracter type, decreased as task difficulty increased, and maximum over the parietal recording sites. The findings indicate that P3a from white noise is robust and should be useful for applied studies as it removes stimulus novelty variability. Theoretical perspectives are discussed.

ERP effects of change localization, change identification, and change blindness

Change blindness is the failure to detect changes in visual scenes. Changes can elicit phenomenologically different perceptual experiences, possibly relating to different mechanisms: changes may be entirely missed, merely detected, located, or identified. We presented sequences of meaningful objects, one of which could change between the presentations. Changes had to be located and identified. Observers sometimes located the change without knowing which object had changed. However, effects of localization with and without identification were remarkably similar on a sequence of event-related potential components (including change-related positivity and N2pc). Only a late contralateral positivity was found exclusively for identified changes, indicating that change localization and change identification initially rely on a common processing sequence and differ only at later stages.

Human Visual System Automatically Encodes Sequential Regularities of Discrete Events

For our adaptive behavior in a dynamically changing environment, an essential task of the brain is to automatically encode sequential regularities inherent in the environment into a memory representation. Recent studies in neuroscience have suggested that sequential regularities embedded in discrete sensory events are automatically encoded into a memory representation at the level of the sensory system. This notion is largely supported by evidence from investigations using auditory mismatch negativity (auditory MMN), an event-related brain potential (ERP) correlate of an automatic memory-mismatch process in the auditory sensory system. However, it is still largely unclear whether or not this notion can be generalized to other sensory modalities. The purpose of the present study was to investigate the contribution of the visual sensory system to the automatic encoding of sequential regularities using visual mismatch negativity (visual MMN), an ERP correlate of an automatic memory-mismatch process in the visual sensory system. To this end, we conducted a sequential analysis of visual MMN in an oddball sequence consisting of infrequent deviant and frequent standard stimuli, and tested whether the underlying memory representation of visual MMN generation contains only a sensory memory trace of standard stimuli (trace-mismatch hypothesis) or whether it also contains sequential regularities extracted from the repetitive standard sequence (regularity-violation hypothesis). The results showed that visual MMN was elicited by first deviant (deviant stimuli following at least one standard stimulus), second deviant (deviant stimuli immediately following first deviant), and first standard (standard stimuli immediately following first deviant), but not by second standard (standard stimuli immediately following first standard). These results are consistent with the regularity-violation hypothesis, suggesting that the visual sensory system automatically encodes sequential regularities. In combination with a wide range of auditory MMN studies, the present study highlights the critical role of sensory systems in automatically encoding sequential regularities when modeling the world.

Event-related brain potential evidence for implicit change detection: a replication of Fernandez-Duque et al. (2003)

Change blindness studies using explicit behavioral measures have revealed that humans are remarkably poor at explicitly detecting changes between two successive visual images until focused attention is drawn to the changes, which supports the notion that outside the range of focused attention, our mental representations of the visual world are so volatile as to be unable to support detection of changes. However, change blindness studies using implicit behavioral measures have revealed that changes outside the range of focused attention might be detected even in the absence of awareness, which supports the possibility that our mental representations are not so volatile as has been suggested. The purpose of the present study was to provide further evidence for implicit change detection using event-related brain potentials (ERPs). For this purpose, we compared ERPs elicited on trials where color changes were present but participants failed to report the presence of changes (Change blindness trials) and ERPs on trials where changes were absent and participants correctly did not report the presence of changes (No-change trials). The result showed that compared to No-change trials, Change blindness trials elicited a frontal/central positivity at around 160-180ms, which is highly consistent with the result of Fernandez-Duque et al. [D. Fernandez-Duque, G. Grossi, I.M. Thornton, H.J. Neville, Representation of change: separate electrophysiolocal markers of attention, awareness, and implicit processing, J. Cogn. Neurosci. 15 (2003) 491-507] who firstly reported an ERP correlate of implicit change detection. This result provides further evidence for implicit change detection, which supports the notion that even outside the range of focused attention, our mental representations of the visual world are robust at least enough to support implicit detection of changes.