23/01/51. Gender-selective effects of the P300 and N400 components of the. VEP waveform. How are ERP related to gender? Event-Related Potential (ERP)

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1 23/01/51 EventRelated Potential (ERP) Genderselective effects of the and N400 components of the visual evoked potential measuring brain s electrical activity (EEG) responded to external stimuli EEG averaging Scott C. Steffensen et al. Vision Research 48 (2008) Brigham Young University, USA 1 EventRelated Potential (ERP) Visual evoked potential (VEP) Auditory evoked potential(aep) Sensory evoked potential(sep) 2 Stimulus onset VEP waveform Positive component Amplitude P100 P200 N200 VEP waveform LP N400 Late VEP components Latency Negative component N50 N100 = ms N400 = ms Late Positive > 400 ms 3 Early VEP components VEP component The component is influenced by the probability that a given object will appear and is a measure of attention allocation (Duncan Johnson et al.,1977) How are ERP related to gender? The previous studies Ehlers et al 2001; Mitchell, et al, 1987; Chu, 1987 Larger amplitudes and shorter latencies in females for early VEP components. The N400 component is thought to reflect contextual integration and is associated with semantic processing under unexpected conditions in both visual and auditory paradigms (Finnigan, Humphreys et al, 2002) In visual and auditory paradigms, it was reported that females have a larger component than males. Hoffman et al.,

2 Polich, 1986, Sangal et al., 1996 There is no significant difference between male and female auditory (Polich, 1986) or visual and auditory (Sangal et al., 1996). The effects of gender on ERP are unclear Objective To further evaluate the effects of gender on VEPs and ERPs evoked by the presentation of relevant and irrelevant stimuli in a visual object recognition task. Relevant stimulus = Target stimulus or interested object 7 8 Materials and Methods Subjects were recruited from undergraduate level neuroscience and psychology courses at Brigham Young University Materials and Methods 15 male and 15 female subjects Age : years (mean age = 22 ± 0.4 years) EEG recording VEP 9 10 EEG/ERP methods Anterior Behavioral task Each subject read a standard set of instructions F1 Fz F2 Left T3 C3 Cz C4 P3 Pz P4 T4 Right verbal explanation A1 O1 Oz O2 A2 Visual stimuli 61 cm 17 monitor Posterior

3 Visual stimuli STANDARD stimulus How did subjects respond? The subjects had to respond to RELEVANT stimulus by pressing a handswitch RELEVANT RELEVANT stimulus IRRELEVANT stimulus STANDARD IRRELEVANT Notrespond Experimental method Experimental method Visual stimuli Blank screen Reaction time(rt) was recorded only when subjects responded to the Relevant stimulus correctly ms If subjects mistakenly responded to the Irrelevant or Standard stimuli within 2 seconds, a NO is shown instead of the RT. If the subject did not respond to a Relevant stimulus within 2 seconds, this resulted in a Missed response. X 15 min NO Handswitch 17 Handswitch 18 3

4 Visual evoked potentials VEP were obtained from all subjects two seconds of EEG around each visual stimulus. Data analysis and statistics The grand averaged potentials at each electrode location revealed that Averaged 54 stimulus presentations for each of the three matrices at each of the electrode positions. Measured the latency and amplitude of each of the peaks of the averaged VEP components. the VEP waveforms evoked at the parietal and occipital electrodes contained the most welldefined combination of early and late components in the Relevant and Irrelevant visual stimuli Data analysis and statistics Measures of reaction time (RT) and VEP components at Oz, O1, O2, P3 and P4 sites were analyzed in all subjects with ANOVA. Paired sample ttests were performed to compare RTs and VEP measurements. Values are expressed as means ± SEM. Statistical significance was expressed at the P < 0.05 level. Result 1.Late components of the VEP are differentially modulated by a response selection 2. Greater and N400 VEP amplitudes in female vs male 3.Laterality Late components of the VEP are differentially modulated by response selection

5 This graph shows superimposed grand averaged VEPs of combined male and female subjects generated at the Oz site. This graph summarizes the effects of response selection on the amplitudes of each VEP component. STIMULUS P100 P200 LP RELEVANT IRRELEVANT STANDARD N50 N200 N400 mean RT 5µV N100 TIME (ms) Greater and N400 VEP amplitudes in female vs male subjects This graph shows superimposed grand averaged VEPs generated at the Oz site by presentation of the Relevant stimulus comparing between male and female subjects. STIMULUS RELEVANT RT =488±11.7 ms RT =509±20.5 ms MALE FEMALE 5µV 27 TIME (ms) 28 This graph summarizes the effects of gender on each of the late amplitude components of the Relevant stimulus. RELEVANT This graph shows superimposed averaged VEPs produced by presentation of the Irrelevant stimulus comparing between male and female subjects. STIMULUS IRRELEVANT MALE FEMALE N400 5µV 29 TIME (ms) 30 5

6 This graph summarizes the effects of gender on the amplitude of the VEP elicited by presentation of the Irrelevant stimulus. IRRELEVANT Laterality This study evaluated the potential for laterality effects that might contribute to the gender differences. Table 1 Amplitude(µv) Latency(ms) Relevant Irrelevant Relevant Irrelevant Table 2 shows the mean amplitudes of the and N400 components of the VEP at the O1, O2, P3, and P4 electrode locations of the standard International system. Amplitude(µv) Relevant Irrelevant Male Female Male Female N400 This table summarized the effects of gender on the amplitude and latency of each components of the VEP that obtained at the Oz site under Relevant and Irrelevant conditions The present study The amplitude of the VEP was enhanced in the relevant stimulus. Discussion amplitude is dependent on the allocation of attentional resources. This result is consistent with previous studies. (Hoffman et al.,1999; Salyer, 2001)

7 N400/LP component This study shown that the N400/LP component produced by the Irrelevant stimulus Hagoort, 2003; Kim et al., 2001; Koyama et al., 1992 The N400 is believed to be part of the brain s response to stimuli that are potentially meaningful, associated with semantic or complex picture processing under noncongruent conditions. Bentin et al.,1985; Deacon et al., 1995; Kim et al., 2001 the N400 appears to be inversely related to the expectancy of a word or stimulus. Koyama et al., 1992; Kutas et al., 2000; Kutas et al., 1998 The N400 has been shown to be reduced by factors that increase the object s predictability within a given context. In this study The visual targets were all equally predictable and parallelprocessed, yet there were differential N400 effect Irrelevant stimulus Why is that? Recognized as not relevant stimulus N400 waveform Make a decision not to response the N400 may be related more to relevancy than predictability, and that an N400 component can be elicited to noncongruent stimuli in a simple object recognition task. In this study noncongruent could mean that the Irrelevant stimuli are not congruent with what the subject was asked to respond to 39 producing a larger N400 component. 40 The LP component usually involved linguistic processing in either visual or auditory paradigms. For example Misra et al., 2003 Late Positive (LP) component found that the LP was only present for repeated words. Stuss et al.,1992 reported that a LP followed the N400 only when the subject responded to picture correctly. 41 Paller et l.,1987; Senkfor et al., 1998 repeated words in incidental learning and correctly recognized old words in recognition tasks elicit larger late positive components than new words. Finnigan et al., 2002 the LP was demonstrated to increase with decision accuracy or decision confidence. 42 7

8 This study used a simple paradigm wherein subjects rarely responded incorrectly The relationship between ERP components and gender difference In this study, it was found that amplitudes associated with the Relevant and Irrelevant stimuli were greater in females than males. they were confident of their responses and therefore the VEP showed an LP component. Supporting previous studies demonstrating that ERPs are sensitive to gender. Chu, 1987; Hoffman et al.,1999 N400 amplitudes were also greater in females than males The relationship between gender and the has been controversial as some studies see no gender bias or larger amplitudes in males. For example Oliver et al., 1999 looked at facial attractiveness and the emotional component, found that amplitudes were greater in male participants. Hypothesis for contradictory findings 1.head size and geometry may account for more of the difference between gender VEPs than actual biological and physiological differences Guthkelch, Bursick, & Sclabassi, seasonal variation and emotion Deldinet al.,1994; Morita et al., 2001; Yamamoto et al., 2000 Morita et al., 2001; Yamamoto et al., 2000 females were found to have larger components when evaluating emotion presented in faces The hemispheric asymmetry (lateralization) might give rise to greater amplitudes in females than males. Roalf, Lowery, & Turetsky, 2006 This study indicates that the N400/LP component of the VEP appears to be a more selective measure of gender than the. In visual recognition task This study did not observe gender differences in hemispheric asymmetry or lateralization that might contribute to the differences between males and females. This obtains despite the lack of differences in the early components of the VEP and in reaction time between males and females sensory processing and motor performance do not contribute to the differences

9 conclusion A:General result (female + male) A1:The amplitude is greatest when subjects respond to Relevant stimuli This might be due to the decision has been made A2:The LP amplitude is greatest when subjects respond to Irrelevant stimuli B:Female vs Male comparison study By response to Relevant stimuli: The amplitudes of and N400 in female subjects are greater than that of male subjects By response e to Irrelevant stimuli: The amplitude of N400 in female subjects is greater than that of male subjects This might be due to a delay of decision making