Júlia Weisz

ERPs and deviance detection: Visual mismatch negativity to repeated visual stimuli

Previous studies showed a visual analogue of the mismatch negativity (MMN) event-related potential (ERP), which is elicited by violating some sensory regularity. Separating physical change from violating a regularity, here we show that the visual MMN (vMMN) is elicited by regularity violations that do not involve physical stimulus change. Adult participants were presented with a series of red-black and green-black checkerboard patterns delivered regularly in an RRGGRRGG ... order. Infrequently (p=0.1) this regularity was broken by repeating a stimulus one additional time (e.g. RRGGRRR). ERPs elicited by irregular stimulus repetitions were negatively displaced compared to those elicited both by regular repetition and regular change in two latency ranges: 100-140 ms and 220-260 ms. Whereas the first of these two negative ERP differences appears to be sensitive to stimulus repetition per se, the second difference can be identified as a vMMN response to violating the sequential regularity. Thus, similarly to its auditory counterpart, vMMN reflects deviance-(regularity-violation) rather than change-detection processes.

Visual temporal window of integration as revealed by the visual mismatch negativity event-related potential to stimulus omissions

We studied whether, similarly to the auditory modality, short-period temporal integration processes occur in vision. Event-related potentials (ERP) were recorded for occasional stimulus omissions from sequences of patterned visual stimuli. A posterior negative component emerged only when the constant stimulus onset asynchrony (SOA) was shorter than 150 ms. This upper limit is comparable with the duration of the temporal window of integration observed in the auditory modality (including experiments studying the effects of stimulus omissions). Parameters of the posterior negativity were highly similar irrespective of whether the stimuli were task-relevant or not (Experiment 1). Thus, we identified this potential as the visual mismatch negativity (vMMN) component, which reflects task-independent detection of violating regularities of the stimulation. vMMN was followed by an anterior positivity (the P3a), indicating attentional shifts induced by the stimulus omissions. In Experiment 2, a posterior negativity similar to that observed in Experiment 1 emerged after the termination of short trains of stimuli, again only when the SOA was shorter than 150 ms. These results support the notion of a temporal integration window in the visual modality, the duration of which is between 150 and 180 ms.

Deviance detection in congruent audiovisual speech: Evidence for implicit integrated audiovisual memory representations

Detection of deviant speech syllables embedded in continuous noise was investigated in an oddball paradigm. Behavioral results showed improvement of detecting and identifying the syllables when congruent visual speech accompanied the utterances. A centrally maximal negative ERP difference wave peaking at approximately 290ms post-stimulus was elicited by audiovisual but not by auditory- or visual-only task-irrelevant deviant syllables. Whereas the circumstances of the elicitation of this ERP response are similar to those of the mismatch negativity component (MMN and its visual counterpart, vMMN), its scalp distribution differs from that of both unimodal MMNs. Elicitation of an MMN-like ERP response (termed here as the audiovisual MMN: avMMN) suggests that detection of the audiovisual deviants involved integrated audiovisual memory representations. The pattern of behavioral and ERP results suggest that the formation of such cross-modal memory representation does not require voluntary operations and may even proceed for stimuli outside the focus of attention.

The influence of cardiac phase on reaction time depending on heart period length and on stimulus and response laterality

The aim of this study was twofold: (1) to reinvestigate the question of cardiac cycle time effect on sensorimotor performance, and (2) to examine the dependence of this effect on stimulus and response laterality. Thirty-eight right-handed subjects performed a simple visual reaction time task, where stimuli were presented randomly to the right or to the left of the fixation point, or centrally. Half of the responses were given by the right hand, and the other half by the left hand. The stimuli occurred at either 150- or 600-msec delays from the R wave of the electrocardiogram, that is, during the systolic or diastolic part of the cardiac cycle, respectively. For right stimuli and right-hand responses, the reaction time was marginally longer for systolic than for diastolic stimuli. No such effect emerged for central and left stimuli and for left-hand responding. This result suggested—albeit weakly—that the sensorimotor functions of the left cerebral hemisphere might be influenced to a greater extent by the physiological changes accompanying cardiac activity than those of the right hemisphere. Additionally, it was shown that in females characterized by long heart periods, the reaction time was longer for stimuli presented during systole than for stimuli presented during diastole, but the opposite was true in females with short heart periods. In males, a similar but nonsignificant tendency was found. This result does not contradict the Laceys’ (1970) baroreceptor hypothesis. The limitations of this and similar approaches are discussed.

Hemispheric preference and lateral eye movements evoked by bilateral visual stimuli

This study investigated the relationship between the direction of lateral eye shifts evoked by bilateral visual stimulation, on the one hand, and verbal vs visuospatial performance, on the other. In males a negative correlation was found between verbal relative to spatial accuracy and the ratio of leftward eye movements. No such relationship was found in females. Additionally, in males body mass index was smaller for those who displayed a greater ratio of leftward eye movements. It was concluded that visually evoked lateral eye shifts might reflect hemispheric preference, similarly as lateral eye movements obtained during the widely used questioning procedure. However, the procedure used in this study for evoking lateral eye shifts seems to be free of some methodological problems of the traditional procedure and is more easy to standardize.