Hales, Kimberly The Effects of Gender on Human Event-Related Potentials Faculty Mentor: Scott C. Steffensen, Psychology Specific components of the human averaged visual evoked potential (VEP) are task-related. As observers scan a visual scene, they use two main types of visual object search: parallel and serial (Luck and Hillyard 1994). Parallel processing is where the object seems to “pop-out” to the observer, while serial processing requires searching. In this study, two targets were used that were previously characterized as parallel or serial (Salyer 2001) to study their differential effects on late VEP components. Gender-related differences in relation to the early components of event-related potentials (ERPs) have often been seen with either lower amplitudes in males and/or shorter latencies in females (Mitchell, Howe et al. 1987; Ehlers, Wall et al. 2001). The aim of this investigation was to further evaluate these effects of gender on ERPs with an emphasis on the late VEP components, particularly the P300 and N400. In these experiments, volunteer subjects’ electroencephalographic (EEG) activity and reaction time were recorded for a paradigm of relevant, irrelevant or standard visual stimuli. The set-up of these subjects included attaching an electrode to the back of the head in the area of the occipital lobe and checking for good impedance (<5000 Ohms). This part of the experiment was usually the only time we would encounter problems, usually because the connection wasn’t solid. For the most part though, this problem was easily fixed by replacing the electrode. Preceding the test run, the each subject was instructed and viewed each type of stimuli and performed a practice run. From this paradigm, the relevant and irrelevant stimuli evoked late VEP components, including the P300, N400, late-positive (LP), and late-negative (LN) potentials that were task-specific and well-discriminated from those of the standard stimulus. The occurrence of the N400 VEP component, seen most prominently and often exclusively in association with the irrelevant stimulus, was unexpected; the N400 is usually implicated in processing wherein novel or unexpected stimuli are presented. As seen in Figure 1, the P300 and N400 amplitudes were significantly greater in females than in males in both the relevant and irrelevant stimuli. In addition, the P300 latencies were shorter in females than males, similar to what others have reported. However, when compared to a similar motivation experiment, male VEPs approached those of females. These results indicate that the N400 can be elicited in tasks requiring symbolic processing of irrelevant, but not unexpected, stimuli and that females process distracting information differently than males. Furthermore, motivational significance of the stimulus/response can modulate specific components of the VEP, perhaps via the enhancement of attentional resources. RELEVANT IRRELEVANT A B STIMULUS STIMULUS MALE MALE 100 FEMALE FEMALE 0 -100 5 µV-200 5 µV 0 400 800 1200 0 400 800 1200 TIME (ms) TIME (ms) C D 20 MALE FEMALE 12 ** MALE FEMALE AMPLITUDE (µV) AMPLITUDE (µV) 10 16 ** * 8 12 8 * 6 4 4 P300 N400 LP LN P300 N400 LP LN Figure 1–The late components of the visual evoked potential are sensitive to gender. (A) This graph shows superimposed averaged VEPs elicited by presentation of the Relevant stimulus and collapsed by gender. The amplitude of the P300 and N400 components of the Relevant VEP waveform appear greater in females than males. (B) This graph shows superimposed averaged VEPs produced by presentation of the Irrelevant stimulus and collapsed by gender. The amplitude of the P300 and N400 components of the Irrelevant VEP appear greater in females than males. (C) This graph summarizes the effects of gender on the amplitude of the VEP elicited by presentation of the Relevant stimulus. Female P300 and N400 amplitudes were significantly greater than males. (D) This graph summarizes the effects of gender on the amplitude of the VEP elicited by presentation of the Irrelevant stimulus. Similarly, female P300 and N400 amplitudes were significantly greater in females than males. . Asterisks * and ** represent significance levels 0.001<P<0.01 and P<0.001, respectively. References: Ehlers, C. L., T. L. Wall, et al. (2001). "Auditory P3 findings in mission Indian youth." J Stud Alcohol 62(5): 562-70. Luck, S. J. and S. A. Hillyard (1994). "Electrophysiological correlates of feature analysis during visual search." Psychophysiology 31(3): 291-308. Mitchell, K. W., J. W. Howe, et al. (1987). "Visual evoked potentials in the older population: age and gender effects." Clin Phys Physiol Meas 8(4): 317-24. Salyer, D. L. (2001). Behavioral (reaction time) and electrophysiological (visual evoked potential) evidence for a parallel-to-serial continuum of visual performance processing: study I and study II. Psychology. Provo, Brigham Young University: 99.
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