The influence of age on the pattern and flash visual evoked magnetic response (VEMR)

The visual evoked magnetic response (VEMR) was measured over the occipital cortex to pattern and flash stimuli in 86 normal subjects aged 15-86 years. The latency of the major positive component (outgoing magnetic field) to the pattern reversal stimulus (P100M) increased with age, particularly after 55 years, while the amplitude of the P100M decreased more gradually over the lifespan. By contrast, the latency of the major positive component to the flash stimulus (P2M) increased more slowly with age after about 50 years, while its amplitude may have decreased in only a proportion of the elderly subjects. The changes in the P100M with age may reflect senile changes in the eye and optic nerve, e.g. senile miosis, degenerative changes in the retina or geniculostriate deficits. The P2M may be more susceptible to senile changes in the visual cortex. The data suggest that the contrast channels of visual information processing deteriorate more rapidly with age than the luminance channels.

Visual evoked magnetic fields to flash and pattern in 100 normal subjects

The practicality of recording visual evoked magnetic fields in 100 subjects 15-87 yr of age using a single channel d.c. SQUID second order gradiometer in an unshielded environment was investigated. The pattern reversal response showed a major positive component between 90 and 120 msec (P100M) while the response to flash produced a major positive component between 90 and 140 msec (P2M). Latency norms of the P100M were more variable than the corresponding P100 and P2 visual evoked potentials. The latency of the P100M may show a steep increase with age in most subjects after about 55 yr whereas only a small trend of latency with age was detected for the flash P2M.

Normative MEG data to flash and pattern reversal stimuli

We have attempted to establish normative values of components of the magnetic evoked field to flash and pattern reversal stimuli prior to clinical use of the MEG. Full visual field, binocular evoked magnetic fields were recorded from 100 subjects 16 to 86 years of age with a single channel dc Squid (BTI) second-order gradiometer at a point 5-6cm above the inion. The majority of subjects showed a large positive component (out going magnetic field) of mean latency 115 ms (SD range 2.5 -11.8 in different decades of life) to the pattern reversal stimulus. In many subjects, this P100M was preceeded and succeeded by negative deflections (in going field). About 6% of subjects showed an inverted response i.e. a PNP wave. Waveforms to flash were more variable in shape with several positive components; the most consistent having a mean latency of 110ms (SD range 6.4-23.2). Responses to both stimuli were consistent when measured on the same subject on six different occasions (SD range 4.8 to 7.3). The data suggest that norms can be established for evoked magnetic field components, in particular for the pattern reversal P100M, which could be used in the diagnosis of neuro-opthalmological disease.

The use of flash and pattern evoked fields in the diagnosis of Alzheimer's disease

Subjects with Alzheimer's disease (AD) exhibit normal visually evoked potentials (VEP) to pattern reversal stimuli but a delayed P2 flash response. The pattern response may originate in the primary visual cortex via the geniculo-calcarine pathway while the flash P2 may originate in the association areas via the cholinergic-tectal pathway. We now show: a) that the pathology of AD is more prominent in the visual association areas B18/19 than in B17 and b) that the magnetic signal to flash and pattern may originate from B18/19 and B17 respectively.

The influence of age on the pattern and flash visual evoked field

We have investigated the effect of ageing on the visual system using the relatively new technique of magentoencephalography (MEG). This technique measures the magnetic signals produced by the visual system using a SQUID magnetometer. The magnetic visual evoked field (VEF) was measured over the occipital cortex to pattern and flash stimuli in 86 normal subjects aged 15 - 86 years. Factors that influenced subject defocussing or defixating the stimulus or selective attention were controlled as far as possible. The latency of the major positive component to the pattern reversal stimulus (P100M) increased with age particularly after the age of 55 years while the amplitude of the P100M decreased over the life span. The latency of the major flash component (P2M) increased much more slowly with age, while its amplitude decreased in only a proportion of elderly subjects. Changes in the P100M with age may reflect senile changes in the eye and optic nerve, e.g. senile miosis or degenerative changes in the retina. The P2M may be more susceptible to senile changes in the retina. The data suggest that the spatial frequency channels deteriorate more rapidly with age than the luminance channels and that MEG may be an effective method of studying ageing in the visual system.

Topography of visual evoked magnetic responses to pattern shift, pattern onset and flash stimuli

Different visual stimuli may activate separate channels in the visual system and produce magnetic responses from the human bran which originate from distinct regions of the visual cortex. To test this hypothesis, we have investigated the distribution of visual evoked magnetic responses to three distinct visual stimuli over the occipital region of the scalp with a DC-SQUID second-order gradiometer in an ubshielded environment. Patterned stimuli were presented full field and to the right half field, while a flash stimulus was presented full field only, in five normal subjects. Magnetic responses were recorded from 20 to 42 positions over the occipital scalp. Topographic maps were prepared of the major positive component within the first 150ms to the three stimuli, i.e., the P100m (pattern shift), C11m (pattern onset) and P2m (flash). For the pattern shift stimulus the data suggested the source of the P100m was close to the midline with the current directed towards the medial surface. The data for the pattern onset C11m suggested a source at a similar depth but with the current directed away from the midline towards the lateral surface. The flash P2m appeared to originate closer to the surface of the occipital pole than both the patterned stimuli. Hence the pattern shift (which may represent movement), and the pattern onset C11m (representing contrast and contour) appear to originate in similar areas of brain but to represent different asepcts of cortical processing. By contrast, the flash P2m (representing luminance change) appears to originate in a distinct area of visual cortex closer to the occipital pole.

Study of the cholinergic factors affecting the flash and pattern reversal visual evoked potentials

The effects of cholinergic agents undergoing clinical trials for the treatment of Alzheimer's disease and the anticholinergic agent scopolamine, were investigated on the components of the flash and pattern reversal visual evoked potentials (VEPs) in young healthy volunteers. The effect of recording the flash and pattern reversal VEPs for 13 hours in 5 healthy male volunteers, revealed no statistically significant change in the latency or amplitude measures. Administration of the muscarinic agonist SDZ 210-086 to 16 healthy male volunteers resulted in the reduction of the flash N2-P2 and pattern reversal N75-P100 peak-to-peak amplitudes. These effects on the flash VEP occurred at both doses (0.5 and 1.0 mg/day), but only at the higher dose on the pattern reversal VEP. Administration of the antimuscarinic agent scopolamine to 11 healthy young male volunteers, resulted in a delay of the flash P2 latency but no effect on the pattern reversal P100 latency. The pattern reversal N75-P100 peak-to-peak amplitude was also increased post dosing. The combination of scopolamine with the acetylcholinesterase inhibitor SDZ ENA 713 resulted in no significant effect on the flash and pattern reversal VEPs, suggesting that the effects of scopolamine may have been partially reversed. Topical application of scopolamine in 6 young healthy volunteers also resulted in no statistically significant effects on the flash and pattern reversal VEPs. The selective effect of scopolamine on the flash P2 latency but not on the pattern reversal P100 latency, provided a model whereby new cholinergic agents developed for the treatment of Alzheimer's disease can be investigated on a physiological basis. In addition, the results of this study led to the hypothesis that the selective flash P2 delay in Alzheimer's disease was probably due to a cholinergic deficit in both the tectal pathway from the retina to the visual cortex and the magnocellular path of the geniculostriate pathway, whereas the lack of an effect on the pattern reversal P100 component was probably due to a sparing of the parvocellular geniculostriate pathway.

The investigation of the primary response of the flash visual evoked response

The topographical distribution of the early components of the flash visual evoked response (VER) were investigated using a twenty channel brain mapping system. Thirty subjects, ranging in age from 21 to 84 years, had flash VERs recorded using the standard 10-20 electrode system to a balanced non-cephalic reference. The subjects were divided into three age groups: a young group, a middle group and an older group. The P2 component (positive component around 100-120 msec) of the flash VER was recorded consistently over the occipital region throughout the age range, as was a frontal negative component (N120) of about the same latency. Only the young age group had this single negative component on the frontage channels, whilst the middle age group showed an additional negative component at around 75 msec (N75). Neither group had a recordable P1 component (positive component around 60-75 msec) over the occipital region. The older age group showed both P1 and P2 components over the occipital region with the distribution of the P1 component being more widespread anteriorly. The frontal channels showed both the negative N75 and the later N120 components. The frontal negative components were shown not to be related to the electroretinogram or the balanced non-cephalic reference, but were affected by the type of stimulation. Responses recorded to both pattern reversal and onset/offset stimulation did not show the frontal negative potentials seen with flash stimulation. It was shown that the P1 component is more readily recordable in the elderly and is preceded during middle age by the development of a frontal negative component at around the same latency. The changing morphology of the negative activity in the frontal region across the age range suggests that the use of an Fz reference would produce an artificial P1 component in the middle age group and an enhancement of this component in the elderly, as well as enhance the P2 component in all ages.

Visual evoked magnetic responses (VEMR) to flash and pattern reversal stimulation

The problems of using a single channel magnetometer (BTi, Model 601) in an unshielded clinical environment to measure visual evoked magnetic responses (VEMR) were studied. VEMR to flash and pattern reversal stimuli were measured in 100 normal subjects. Two components, the P100M to pattern reversal and P2M to flash, were measured successfully in the majority of patients. The mean latencies of these components in different decades of life were more variable than the visual evoked potentials (VEP) that have been recorded to these stimuli. The latency of the P100M appeared to increase significantly after about 55 years of age whereas little change occurred for the flash P2M. The effects of blur, check size, stimulus size and luminance intensity on the latency and amplitude of the VEMR were studied. Blurring a small (32') check significantly increased latency whereas blurring a large (70') check had little effect on latency. Increasing check size significantly reduced latency of the P100M but had little effect on amplitude. Increasing the field size decreases the latency and increases the amplitude of the P100M. Within a normal subject, most of the temporal variability of the P100M appeared to be associated with run to run variation rather than between recording sessions on the same day or between days. Reproducibility of the P100M was improved to a degree by employing a magnetically shielded room. Increasing flash intensity decreases the latency and increases the amplitude of the P2M component. The magnitude of the effects of varying stimulus parameters on the VEMR were frequently greater than is normally seen in the VEP. The topography of the P100M and P2M varied over the scalp in normal subjects. Full field responses to a large check could be explained as approximately the sum of the half field responses and were consistent with the cruciform model of the visual cortex. Preliminary source localisation data suggested a shallower source in the visual cortex for the flash P2M compared with the P100M. The data suggest that suitable protocols could be devised to obtain normative data of sufficient quality to use the VEMR to flash and pattern clinically.

Utilising fiction to promote english language acquisition

Towards the end of the university stage, students residing in the United Arab Emirates and specialising in subjects other than English are expected- amongst other university requirements- to have acquired adequate communicative competence as well as a repertoire of critical thinking skills. Despite the efforts made within the field of teaching English to EFL university students in the country, the output gained in terms of acquired skills and competencies is still below expectations. The main concerns of the current thesis are, therefore, a) to investigate the factors which inhibit EFL university students’ progress in the areas of acquiring adequate communicative competence as well as critical thinking skills, and b) to propose a course book and pedagogic methods to improve students’ progress in the areas of acquiring adequate communicative competence as well as critical thinking skills. Believing in the essential role literature plays in enhancing critical thinking and promoting communicative competence on the part of EFL learners, the current study introduces a course, designed and implemented by the researcher: LEARN AND GAIN. The proposed course is fiction-based language teaching, adopting the view that literature is a resource rather than an object, thus advocating the use of literature as one of the main resources in foreign/second language acquisition. Investigating whether or not the proposed course was effective in promoting EFL university students’ communicative competence as well as enhancing their critical thinking skills, a study sample taken from the study population was selected. Adopting an experimental design, the research project involved two groups: experimental and control. The experimental group students were exposed to the proposed course whilst the control group students were exposed to a general English language course. To examine treatment effectiveness, the researcher set and administered a pre-post test. Divided into two main parts, communicative critical reading competence and communicative critical writing competence, the pre-post test measured subjects’ communicative critical reading competence and subjects’ communicative critical writing competence. In addition, a pre-post questionnaire was administered and a semi-structured interview was conducted involving the experimental group students, to gain an awareness of students’ attitudes towards learning literary texts in general, and the proposed course in particular. To examine issues of interest and relevance, gender differences: male vs. female, and university major: science vs. non-science, were also examined for enrichment purposes. For the purpose of gathering sufficient data about subjects’ achievements on the pre-post, the following statistical tests were conducted: Mann-Whitney test, and paired data t-test. Based on the statistical findings, the experimental group students’ performance on the communicative critical reading competence pre-post test and the communicative critical writing competence pre-post test was significantly better than their counterparts of the control group students. Speaking of gender differences in relation to language performance on the communicative critical reading competence pre-post test and the communicative critical writing competence pre-post test, no significant differences were cited. Neither did the researcher cite any significant performance differences between science/non-science students on the communicative critical reading competence pre-post test and the communicative critical writing competence pre-post test. As far as the questionnaire’s findings are concerned, the experimental group students’ responses to the post-questionnaire’s items were more positive than those of their responses to the pre-questionnaire’s, thus indicating some positive attitudes towards literature, which students possibly gained throughout the course of implementation. Relating the discussion to the interview’s results, students conveyed their satisfaction with the proposed course, emphasising that promoting English language skills through the use of literary texts was rewarding. In the light of findings and conclusions, a number of recommendations as well as implications have been proposed. The current study aimed to arrive at some appropriate suggestions to a number of enquiries, yet concluding with some areas of enquiry to be explored for further research.

Characteristics of motor resonance predict the pattern of flash-lag effects for biological motion

Background - When a moving stimulus and a briefly flashed static stimulus are physically aligned in space the static stimulus is perceived as lagging behind the moving stimulus. This vastly replicated phenomenon is known as the Flash-Lag Effect (FLE). For the first time we employed biological motion as the moving stimulus, which is important for two reasons. Firstly, biological motion is processed by visual as well as somatosensory brain areas, which makes it a prime candidate for elucidating the interplay between the two systems with respect to the FLE. Secondly, discussions about the mechanisms of the FLE tend to recur to evolutionary arguments, while most studies employ highly artificial stimuli with constant velocities. Methodology/Principal Finding - Since biological motion is ecologically valid it follows complex patterns with changing velocity. We therefore compared biological to symbolic motion with the same acceleration profile. Our results with 16 observers revealed a qualitatively different pattern for biological compared to symbolic motion and this pattern was predicted by the characteristics of motor resonance: The amount of anticipatory processing of perceived actions based on the induced perspective and agency modulated the FLE. Conclusions/Significance - Our study provides first evidence for an FLE with non-linear motion in general and with biological motion in particular. Our results suggest that predictive coding within the sensorimotor system alone cannot explain the FLE. Our findings are compatible with visual prediction (Nijhawan, 2008) which assumes that extrapolated motion representations within the visual system generate the FLE. These representations are modulated by sudden visual input (e.g. offset signals) or by input from other systems (e.g. sensorimotor) that can boost or attenuate overshooting representations in accordance with biased neural competition (Desimone & Duncan, 1995).

Flash pyrolysis of biomass for liquid fuels

DUE TO COPYRIGHT RESTRICTIONS ONLY AVAILABLE FOR CONSULTATION AT ASTON UNIVERSITY LIBRARY AND INFORMATION SERVICES WITH PRIOR ARRANGEMENT