Visual Evoked Potentials: Analysis of the Fovea and Perifovea

Visual evoked potentials (VEP) were used to measure how stimulus properties (pattern VEP check sizes/spatial frequency) and retinal eccentricity (fovea versus perifovea) interact to give rise to the final VEP response. The purposes of this study were to investigate how stimulus check size (spatial frequencies) and retinal eccentricity affect the VEP response, re-examine whether the cortical magnification factor is applicable to VEP measures, and to determine optimal sized VEP checks for foveal and perifoveal stimuli. In this study, we used a foveal target that was a two degree circle with a diameter of 3.6 cm; a perifoveal target that was a circular ten degree annulus with an inner diameter of 3.6 cm and an outer diameter of 17.5 cm; and a full field target that was a ten degree circle with a diameter of 17.5 cm. These stimuli were chosen because they stimulate approximately the same amount of cortical area. VEPs were performed on ten healthy adult subjects monocularly through the dominant eye. Measurements of the implicit time (N1 and P1) and amplitude (N1-P1) were taken using four different VEP check sizes, 0.23, 0.52, 0.83, and 1.78 degrees). The findings of this study indicate that differences exist in sensitivity to specific check sizes (spatial frequencies) depending on the type of VEP measure used (implicit time or amplitude) and area of retina stimulated. These results are not consistent with a single stimulus being optimal for all measures and that there is a complex interaction between visual targets and responses

Defective chromatic and achromatic visual pathways in developmental dyslexia: Cues for an integrated intervention programme.

Abstract PURPOSE: As well as obtaining confirmation of the magnocellular system involvement in Developmental dyslexia (DD); the aim was primarily to search for a possible involvement of the parvocellular system; and, furthermore, to complete the assessment of the visual chromatic axis by also analysing the koniocellular system. METHODS: Visual evoked potentials (VEPs) in response to achromatic stimuli with low luminance contrast and low spatial frequency, and isoluminant red/green and blue/yellow stimuli with high spatial frequency were recorded in 10 dyslexic children and 10 age- and sex-matched, healthy subjects. RESULTS: Dyslexic children showed delayed VEPs to both achromatic stimuli (magnocellular-dorsal stream) and isoluminant red/green and blue/yellow stimuli (parvocellular-ventral and koniocellular streams). To our knowledge, this is the first time that a dysfunction of colour vision has been brought to light in an objective way (i.e., by means of electrophysiological methods) in children with DD. CONCLUSION: These results give rise to speculation concerning the need for a putative approach for promoting both learning how to read and/or improving existing reading skills of children with or at risk of DD. The working hypothesis would be to combine two integrated interventions in a single programme aimed at fostering the function of both the magnocellular and the parvocellular streams

Predicting the effect of interspecific competition on habitat suitability for the endangered african wild dog under future climate and land cover changes

Apex predators play an important role in regulating ecological interactions, and therefore their loss can affect biodiversity across trophic levels. Large carnivores have experienced substantial population and range declines across Africa, and future climate change is likely to amplify these threats. Hence it is important to understand how future environmental changes will affect their long-term habitat suitability and population persistence. This study aims to identify the factors limiting the distribution of the endangered African wild dog,Lycaon pictus,and determine how biotic interactions and changing climate and land cover will affect future range suitability. We use Species Distribution Models (SDMs) to predict the current and future distribution of suitable conditions forL. pictusand its dominant competitorPanthera leo. We show that range suitability forL. pictusis limited by climatic and land cover variables, as well as high niche and range overlap withP. leo. Although both species are predicted to experience range contractions under future climate change,L. pictusmay benefit from release from the effect of interspecific competition in eastern and central parts of its range. Our study highlights the importance of including land cover variables with corresponding future projections and incorporating the effects of competing species when predicting the future distribution of species whose ranges are not solely limited by climate. We conclude that SDMs can help identify priority areas for the long-term conservation of large carnivores, and therefore should be used to inform adaptive conservation management in face of future climate change

Studying death and near-death experiences requires neuroscientific expertise

peer reviewedParnia et al.1 recently published suggestions for the study of death and experiences recalled in a near-death context. We have serious reservations about the authors’ statements. In this commentary, we discuss the omissions and knowledge gaps inherent to the authors’ paper, which among others include incorrect neurological claims about brain death and misunderstandings regarding the terminology of consciousness. Although we believe that (near-)death research deserves a framework guideline, the paper by Parnia and colleagues is misleading and, contrary to the authors' intention, hinders the scientific understanding of near-death experiences and the neural mechanisms occurring in the dying brain

High frequency oscillations as a correlate of visual perception

“NOTICE: this is the author’s version of a work that was accepted for publication in International journal of psychophysiology. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in International journal of psychophysiology , 79, 1, (2011) DOI 10.1016/j.ijpsycho.2010.07.004Peer reviewedPostprin

Predicting the effect of interspecific competition on habitat suitability for the endangered African wild dog under future climate and land cover changes

Apex predators play an important role in regulating ecological interactions, and therefore their loss can affect biodiversity across trophic levels. Large carnivores have experienced substantial population and range declines across Africa, and future climate change is likely to amplify these threats. Hence it is important to understand how future environmental changes will affect their long-term habitat suitability and population persistence. This study aims to identify the factors limiting the distribution of the endangered African wild dog, Lycaon pictus, and determine how biotic interactions and changing climate and land cover will affect future range suitability. We use Species Distribution Models (SDMs) to predict the current and future distribution of suitable conditions for L. pictus and its dominant competitor Panthera leo. We show that range suitability for L. pictus is limited by climatic and land cover variables, as well as high niche and range overlap with P. leo. Although both species are predicted to experience range contractions under future climate change, L. pictus may benefit from release from the effect of interspecific competition in eastern and central parts of its range. Our study highlights the importance of including land cover variables with corresponding future projections and incorporating the effects of competing species when predicting the future distribution of species whose ranges are not solely limited by climate. We conclude that SDMs can help identify priority areas for the long-term conservation of large carnivores, and therefore should be used to inform adaptive conservation management in face of future climate change

Role of Therapeutic Devices in Enhancing Speech Intelligibility and Vocal Intensity in an Individual with Parkinson’s Disease

The prevailing speech therapy techniques for treating hypokinetic dysarthria in individuals with Parkinson\u27s disease (PD) yields improvements within the clinical setting, however, maintenance and generalization of acquired behaviors continue to be a challenge. The purpose of this study was to investigate the effects of portable therapeutic devices including Ambulatory Phonation Monitor with biofeedback (APM) and auditory masker in maintenance and carryover of improved speech. Our participant was an individual diagnosed with PD for the past 25 years who continued to display speech disturbances despite undergoing several behavioral speech therapy programs and neurosurgical procedures. Speech intelligibility and average intensity measures under automatic, elicited, and spontaneous speech tasks were recorded pre- and postusage of APM and auditory masker for a period of 1 week each. Preliminary findings showed no significant difference in the measures between means (P\u3e0.05) across all tasks for both the devices. Suggestions for future research on therapeutic devices are discussed

Interhemispheric transfer and the processing of foveally presented stimuli

A review of the literature shows that the LVF and the RVF do not overlap. This means that foveal representations of words are effectively split and that interhemispheric communication is needed to recognise centrally presented words

Defective chromatic and achromatic visual pathways in developmental dyslexia : Cues for an integrated intervention programme

Purpose: As well as obtaining confirmation of the magnocellular system involvement in developmental dyslexia (DD); the aim was primarily to search for a possible involvement of the parvocellular system; and, furthermore, to complete the assessment of the visual chromatic axis by also analysing the koniocellular system. Methods: Visual evoked potentials (VEPs) in response to achromatic stimuli with low luminance contrast and low spatial frequency, and isoluminant red/green and blue/yellow stimuli with high spatial frequency were recorded in 10 dyslexic children and 10 age- and sex-matched, healthy subjects. Results: Dyslexic children showed delayed VEPs to both achromatic stimuli (magnocellular-dorsal stream) and isoluminant red/green and blue/yellow stimuli (parvocellular-ventral and koniocellular streams). To our knowledge, this is the first time that a dysfunction of colour vision has been brought to light in an objective way (i.e., by means of electrophysiological methods) in children with DD. Conclusion: These results give rise to speculation concerning the need for a putative approach for promoting both learning how to read and/or improving existing reading skills of children with or at risk of DD. The working hypothesis would be to combine two integrated interventions in a single programme aimed at fostering the function of both the magnocellular and the parvocellular streams