Potentials generated by the eye cause unwanted artifact in Visual Evoked Response (VER) recordings. These artifacts often contaminate the data in a systematic way that can lead to spurious experimental results. Although it is widely agreed that ocular artifact must be accounted for, the methods used to deal with this problem are varied. The present study compared four methods used to control ocular artifact; blink rejection, eyes closed, subtraction and regression. Twenty normal, female subjects were tested twice within the same session. Subjects watched light flashes of 4 intensities; 2, 30, 80, and 240 ft lamberts. The lights were presented at 1 hertz, reached maximum brightness in 0.5 msec and lasted for 0.5 sec. During testing the VER, and electroocculographic (EOG) response generated by a blink, were recorded. In the blink rejection method, any VER epoch that contained blink artifact was excluded from the average. The eyes closed method consisted of having subjects watch the stimuli through closed eyelids. The subtraction method corrects blink artifact by digitally subtracting the averaged EOG from the EEG. The proportion of EOG subtracted was determined by the EEG/EOG ratio estimated while subjects blinked spontaneously in a darkened environment. The regression method determines what proportion of EOG is to be subtracted on the basis of the correlation between EOG and EEG within VER epochs. Two correction, factors are calculated, one to correct for vertical movements and one to correct for horizontal movements. The blink rejection method was found to be useful with subjects who had 40% or more blink-free epochs, but was an unreliable method for the majority of subjects. The eyes closed method was also found to produce poor VER data. The eyelids appear to attenuate the light reaching the retina and there may be eyeball movement despite having the eyes closed. Both the subtraction and regression methods substantially reduced the ocular artifact. Horizontal eye movements do not appear to be a significant problem over the short intervals of VER recording because the regression method was not superior to the subtraction method in removing artifact. Although the subtraction and regression methods effectively reduce ocular artifact, both are less effective at posterior electrode placements. The reason for this may be that ocular potential is not propagated across the scalp in a linear fashion, as often assumed. Using spontaneously generated blinks in a darkened environment, it was found that the ocular potential waveform changes shape as it moves towards the back of the head. / Arts, Faculty of / Psychology, Department of / Graduate

Previous studies have found that spatial processing in children and adults with Down syndrome is different in comparison to the normal population. Some previous studies have also found that there is a high prevalence of colour vision deficiencies in people with Down syndrome. The aim of the present study was to use an objective test, the transient visual evoked potential (VEP), to assess achromatic and chromatic visual processing in adults with Down syndrome. Achromatic VEPs were recorded in response to black-white stimuli presented in patternreversal mode. Chromatic VEPs were recorded in response to two types of colour pattern, presented in pattern onset-offset mode. The two colour types were intended to preferentially stimulate the two principal chromatic pathways of the visual system, the ???redgreen??? and ???blue-yellow??? colour-opponent pathways. These stimuli are here termed the ???LM??? and ???S-(L+M) stimuli, respectively, reflecting the cone types that input to the pathways they are intended to stimulate. Each subject also completed two subjective colour vision tests, the Colour Vision Test Made Easy (CVTME) and the City University Colour Vision Test (CUT). Morphology of the achromatic and chromatic VEPs was found to differ between the group with Down syndrome and an age-matched control group. The latency of the P100 component of the achromatic VEP was found to be significantly later in the group with Down syndrome compared to the control group (the N75 latency was earlier in the group with Down syndrome, but not significantly so). The group-averaged peak-to-peak amplitude of the achromatic VEP was significantly lower in the group with Down syndrome compared to the control group. The major positive component of the VEP in response to the L-M stimulus was of significantly longer latency compared to that of the control group. The major negative component and the peak-to-peak amplitude of this response were not significantly different between the groups. For the response to S-(L+M) stimuli, the latency of the major negativity was significantly earlier in the group with Down syndrome and the major positivity was later, but not significantly so. Amplitude of this response was significantly higher in adults with Down syndrome compared to the control group. Most subjects in both groups passed both the CVTME and CUT. Our findings indicate that chromatic VEPs are abnormal in Down syndrome, and this may reflect abnormal processing of chromatic stimuli in this population. Alternatively, these abnormalities may arise due to abnormal cortical morphology, which may occur with normal or abnormal processing of chromatic signals. These findings further indicate that abnormality of chromatic VEPs may be expected in Down syndrome, and is not necessarily indicative of pathology or other abnormal function that is unrelated to the syndrome.

Previous studies have found that spatial processing in children and adults with Down syndrome is different in comparison to the normal population. Some previous studies have also found that there is a high prevalence of colour vision deficiencies in people with Down syndrome. The aim of the present study was to use an objective test, the transient visual evoked potential (VEP), to assess achromatic and chromatic visual processing in adults with Down syndrome. Achromatic VEPs were recorded in response to black-white stimuli presented in patternreversal mode. Chromatic VEPs were recorded in response to two types of colour pattern, presented in pattern onset-offset mode. The two colour types were intended to preferentially stimulate the two principal chromatic pathways of the visual system, the ???redgreen??? and ???blue-yellow??? colour-opponent pathways. These stimuli are here termed the ???LM??? and ???S-(L+M) stimuli, respectively, reflecting the cone types that input to the pathways they are intended to stimulate. Each subject also completed two subjective colour vision tests, the Colour Vision Test Made Easy (CVTME) and the City University Colour Vision Test (CUT). Morphology of the achromatic and chromatic VEPs was found to differ between the group with Down syndrome and an age-matched control group. The latency of the P100 component of the achromatic VEP was found to be significantly later in the group with Down syndrome compared to the control group (the N75 latency was earlier in the group with Down syndrome, but not significantly so). The group-averaged peak-to-peak amplitude of the achromatic VEP was significantly lower in the group with Down syndrome compared to the control group. The major positive component of the VEP in response to the L-M stimulus was of significantly longer latency compared to that of the control group. The major negative component and the peak-to-peak amplitude of this response were not significantly different between the groups. For the response to S-(L+M) stimuli, the latency of the major negativity was significantly earlier in the group with Down syndrome and the major positivity was later, but not significantly so. Amplitude of this response was significantly higher in adults with Down syndrome compared to the control group. Most subjects in both groups passed both the CVTME and CUT. Our findings indicate that chromatic VEPs are abnormal in Down syndrome, and this may reflect abnormal processing of chromatic stimuli in this population. Alternatively, these abnormalities may arise due to abnormal cortical morphology, which may occur with normal or abnormal processing of chromatic signals. These findings further indicate that abnormality of chromatic VEPs may be expected in Down syndrome, and is not necessarily indicative of pathology or other abnormal function that is unrelated to the syndrome.

Diss. (sammanfattning) Linköping : Linköpings universitet, 2006. / Härtill 5 uppsatser.

No description available.

OBJETIVO: Avaliar a capacidade do potencial visual evocado multifocal (PEV-mf) em diferenciar pacientes portadores de hemianopsia temporal de controles normais e avaliar a correlação entre o PEV-mf, o campo visual (CV) realizado com a perimetria automatizada e a tomografia de coerência óptica de domínio fourier (TCO-dF). MÉTODOS: Vinte sete olhos de 21 pacientes com defeito de campo visual temporal secundário a compressão quiasmática e 43 olhos de 23 controles normais foram submetidos aos exames PEV-mf, CV e TCO-dF (3D OCT-1000®, Topcon) da mácula e da camada de fibras nervosas da retina (CFNR). Foi calculada a média das respostas do PEV-mf global, do PEV-mf central e a média de espessura do TCO-dF da mácula para cada quadrante e para cada hemicampo, enquanto a espessura da CFNR foi dividida em 12 setores ao redor do nervo óptico. A perda de CV foi calculada para os quatro quadrantes e para os hemicampos temporal e nasal no CV 24-2 e CV 10-2. Os dois grupos foram comparados utilizando equações de estimativas generalizadas (GEE) e as correlações entre o PEV-mf, CV e o TCO-dF foram calculadas. RESULTADOS: As médias das amplitude P1 e N2 do PEV-mf global e central para os hemicampos e os quadrantes temporais foram significativamente menores nos pacientes que nos controles (p < 0.004). Não houve diferença estatística entre os grupos para os parâmetros de amplitudes do PEV-mf nos setores nasais. Não houve diferença estatística nas médias das latências do PEV-mf global e central entre os pacientes e os controles normais. Foi encontrada correlação moderada, estatisticamente significativa, entre os parâmetros de amplitudes temporais do PEV-mf - global e central com a perda de CV 24-2 e 10-2 temporal, assim como com as medidas de espessura macular e da espessura CFNR na TCO-dF. CONCLUSÕES: As médias das amplitudes do PEV-mf foram capazes de diferenciar olhos de pacientes com hemianopsia dos controles normais e apresentaram correlação significativa com os dados obtidos pela perimetria automatizada e pelo TCO-dF. Estes dados sugerem que o PEV-mf global e central podem ser utilizados na detecção de anormalidades do campo visual em pacientes portadores de compressão quiasmática / PURPOSE: To evaluate the ability of multifocal visual evoked potential (mfVEP) to differentiate patients with temporal hemianopia due to chiasmal compression from normal controls. To assess the relationship between mfVEP, standard automated perimetry (SAP) and fourier domain-optical coherence tomography (fd-OCT). METHODS: Twenty-seven eyes of 21 patients with permanent temporal visual field (VF) defects from chiasmal compression and 43 eyes of 23 healthy controls underwent mfVEP, SAP and fd-OCT (3D OCT-1000®, Topcon) macular and peripapillary retinal nerve fiber layer (RNFL) measurements. It was averaged the responses for global mfVEP, central mfVEP and fd-OCT macular measurements were averaged in quadrants and halves, while peripapillary RNFL thickness was averaged in 12 sectors around the disc. VF loss was estimated in four quadrants and each half of 24-2 and 10-2 strategy test points. The two groups were compared using generalized estimated equations (GEE). Correlations between mfVEP, VF and fd-OCT findings were verified. RESULTS: Global and central mfVEP P1 and N2 amplitude parameters of temporal measurements were significantly smaller in patients than controls (p < 0.004). No significant differences were observed between the groups with respect to mfVEP amplitude parameters from the nasal measurements. No significant differences were observed in global and central mfVEP latency parameters for all averaged measurements between patients and healthy controls. A significant moderate correlation was found between global and central mfVEP amplitude parameters of temporal measurements and temporal VF 24-2 and 10-2 loss as well as with corresponding fd-OCT macular and RNFL thickness measurements. CONCLUSIONS: mfVEP amplitude parameters were able to differentiate eyes with temporal hemianopia from controls and were significant correlated with VF and fd-OCT findings. These data suggest that it is a useful technology for detecting visual abnormalities in patients with chiasmal compression

OBJETIVO: Avaliar a capacidade do potencial visual evocado multifocal (PEV-mf) em diferenciar pacientes portadores de hemianopsia temporal de controles normais e avaliar a correlação entre o PEV-mf, o campo visual (CV) realizado com a perimetria automatizada e a tomografia de coerência óptica de domínio fourier (TCO-dF). MÉTODOS: Vinte sete olhos de 21 pacientes com defeito de campo visual temporal secundário a compressão quiasmática e 43 olhos de 23 controles normais foram submetidos aos exames PEV-mf, CV e TCO-dF (3D OCT-1000®, Topcon) da mácula e da camada de fibras nervosas da retina (CFNR). Foi calculada a média das respostas do PEV-mf global, do PEV-mf central e a média de espessura do TCO-dF da mácula para cada quadrante e para cada hemicampo, enquanto a espessura da CFNR foi dividida em 12 setores ao redor do nervo óptico. A perda de CV foi calculada para os quatro quadrantes e para os hemicampos temporal e nasal no CV 24-2 e CV 10-2. Os dois grupos foram comparados utilizando equações de estimativas generalizadas (GEE) e as correlações entre o PEV-mf, CV e o TCO-dF foram calculadas. RESULTADOS: As médias das amplitude P1 e N2 do PEV-mf global e central para os hemicampos e os quadrantes temporais foram significativamente menores nos pacientes que nos controles (p < 0.004). Não houve diferença estatística entre os grupos para os parâmetros de amplitudes do PEV-mf nos setores nasais. Não houve diferença estatística nas médias das latências do PEV-mf global e central entre os pacientes e os controles normais. Foi encontrada correlação moderada, estatisticamente significativa, entre os parâmetros de amplitudes temporais do PEV-mf - global e central com a perda de CV 24-2 e 10-2 temporal, assim como com as medidas de espessura macular e da espessura CFNR na TCO-dF. CONCLUSÕES: As médias das amplitudes do PEV-mf foram capazes de diferenciar olhos de pacientes com hemianopsia dos controles normais e apresentaram correlação significativa com os dados obtidos pela perimetria automatizada e pelo TCO-dF. Estes dados sugerem que o PEV-mf global e central podem ser utilizados na detecção de anormalidades do campo visual em pacientes portadores de compressão quiasmática / PURPOSE: To evaluate the ability of multifocal visual evoked potential (mfVEP) to differentiate patients with temporal hemianopia due to chiasmal compression from normal controls. To assess the relationship between mfVEP, standard automated perimetry (SAP) and fourier domain-optical coherence tomography (fd-OCT). METHODS: Twenty-seven eyes of 21 patients with permanent temporal visual field (VF) defects from chiasmal compression and 43 eyes of 23 healthy controls underwent mfVEP, SAP and fd-OCT (3D OCT-1000®, Topcon) macular and peripapillary retinal nerve fiber layer (RNFL) measurements. It was averaged the responses for global mfVEP, central mfVEP and fd-OCT macular measurements were averaged in quadrants and halves, while peripapillary RNFL thickness was averaged in 12 sectors around the disc. VF loss was estimated in four quadrants and each half of 24-2 and 10-2 strategy test points. The two groups were compared using generalized estimated equations (GEE). Correlations between mfVEP, VF and fd-OCT findings were verified. RESULTS: Global and central mfVEP P1 and N2 amplitude parameters of temporal measurements were significantly smaller in patients than controls (p < 0.004). No significant differences were observed between the groups with respect to mfVEP amplitude parameters from the nasal measurements. No significant differences were observed in global and central mfVEP latency parameters for all averaged measurements between patients and healthy controls. A significant moderate correlation was found between global and central mfVEP amplitude parameters of temporal measurements and temporal VF 24-2 and 10-2 loss as well as with corresponding fd-OCT macular and RNFL thickness measurements. CONCLUSIONS: mfVEP amplitude parameters were able to differentiate eyes with temporal hemianopia from controls and were significant correlated with VF and fd-OCT findings. These data suggest that it is a useful technology for detecting visual abnormalities in patients with chiasmal compression