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311 results on '"Erichsen, Jonathan"'

51. Saccades and fixations in children with delayed reading skills

Author

Universitat Politècnica de Catalunya. Departament d'Òptica i Optometria, Viñuela Navarro, Valldeflors, Erichsen, Jonathan, Williams, Cathy, Woodhouse, Margaret, Universitat Politècnica de Catalunya. Departament d'Òptica i Optometria, Viñuela Navarro, Valldeflors, Erichsen, Jonathan, Williams, Cathy, and Woodhouse, Margaret

Abstract

Purpose: Previous studies have reported that eye movements differ between good/average and poor readers. However, these studies have been limited to investigating eye movements during reading related tasks, and thus, the differences found could arise from deficits in higher cognitive processes involved in reading rather than oculomotor performance. The purpose of the study is to determine the extent to which eye movements in children with delayed reading skills are different to those obtained from children with good/average reading skills in non-reading related tasks. Methods: After a screening optometric assessment, eye movement recordings were obtained from 120 children without delayed reading skills and 43 children with delayed reading skills (4 to 11 years) using a Tobii TX300 eye tracker. Cartoon characters were presented horizontally from -20° to +20° in steps of 5° to study saccades. An animated stimulus in the centre of the screen was presented for 8 seconds to study fixation stability. Saccadic main sequences, and the number and amplitude of the saccades during fixation were obtained for each participant. Children with delayed reading skills (n = 43) were unmasked after data collection was completed. Medians and quartiles were calculated for each eye movement parameter for children without (n = 120) and with (n = 43) delayed reading skills. Results: Independent t-tests with Bonferroni correction showed no significant differences in any of the saccadic main sequence parameters (Slope, Intercept, A, n and Q ratio) between children without and with delayed reading (p > 0.01). Similarly, no significant differences were found in the number of saccades and their amplitude during the fixation task between the two groups (p > 0.05). Further, none of the gross optometric parameters assessed (visual acuity, refractive error, ocular alignment, convergence, stereopsis and accommodation accuracy) were found to be associated with delayed reading skills (p > 0.05). Conclu, Peer Reviewed, Postprint (author's final draft)

Published
2017

52. Effect of stimulus type and motion on smooth pursuit in adults and children

Author

Universitat Politècnica de Catalunya. Departament d'Òptica i Optometria, Universitat Politècnica de Catalunya. VOS - Visió, Optometria i Salut, Viñuela Navarro, Valldeflors, Erichsen, Jonathan, Williams, Cathy, Woodhouse, Margaret, Universitat Politècnica de Catalunya. Departament d'Òptica i Optometria, Universitat Politècnica de Catalunya. VOS - Visió, Optometria i Salut, Viñuela Navarro, Valldeflors, Erichsen, Jonathan, Williams, Cathy, and Woodhouse, Margaret

Abstract

Purpose: This study presents a two-degree customized animated stimulus developed to evaluate smooth pursuit in children and investigates the effect of its predetermined characteristics (stimulus type and size) in an adult population. Then, the animated stimulus is used to evaluate the impact of different pursuit motion paradigms in children. Methods: To study the effect of animating a stimulus, eye movement recordings were obtained from 20 young adults while the customized animated stimulus and a standard dot stimulus were presented moving horizontally at a constant velocity. To study the effect of using a larger stimulus size, eye movement recordings were obtained from 10 young adults while presenting a standard dot stimulus of different size (1° and 2°) moving horizontally at a constant velocity. Finally, eye movement recordings were obtained from 12 children while the 2° customized animated stimulus was presented after three different smooth pursuit motion paradigms. Performance parameters, including gains and number of saccades, were calculated for each stimulus condition. Results: The animated stimulus produced in young adults significantly higher velocity gain (mean: 0.93; 95% CI: 0.90-0.96; P = .014), position gain (0.93; 0.85-1; P = .025), proportion of smooth pursuit (0.94; 0.91-0.96, P = .002), and fewer saccades (5.30; 3.64-6.96, P = .008) than a standard dot (velocity gain: 0.87; 0.82-0.92; position gain: 0.82; 0.72-0.92; proportion smooth pursuit: 0.87; 0.83-0.90; number of saccades: 7.75; 5.30-10.46). In contrast, changing the size of a standard dot stimulus from 1° to 2° did not have an effect on smooth pursuit in young adults (P > .05). Finally, smooth pursuit performance did not significantly differ in children for the different motion paradigms when using the animated stimulus (P > .05). Conclusions: Attention-grabbing and more dynamic stimuli, such as the developed animated stimulus, might potentially be useful for eye movement research. Finally, Peer Reviewed, Postprint (author's final draft)

Published
2017

53. Infantile nystagmus: an optometrist’s perspective

Author

Zahidi,Asma AA, Woodhouse,J Margaret, Erichsen,Jonathan T, Dunn,Matt J, Zahidi,Asma AA, Woodhouse,J Margaret, Erichsen,Jonathan T, and Dunn,Matt J

Abstract

Asma AA Zahidi, J Margaret Woodhouse, Jonathan T Erichsen, Matt J Dunn Research Unit for Nystagmus, School of Optometry and Vision Sciences, Cardiff University, Cardiff, UK Abstract: Infantile nystagmus (IN), previously known as congenital nystagmus, is an involuntary to-and-fro movement of the eyes that persists throughout life. IN is one of three types of early-onset nystagmus that begin in infancy, alongside fusion maldevelopment nystagmus syndrome and spasmus nutans syndrome. Optometrists may also encounter patients with acquired nystagmus. The features of IN overlap largely with those of fusion maldevelopment nystagmus syndrome, spasmus nutans syndrome, and acquired nystagmus, yet the management for each subtype is different. Therefore, the optometrist’s role is to accurately discern IN from other forms of nystagmus and to manage accordingly. As IN is a lifelong condition, its presence not only affects the visual function of the individual but also their quality of life, both socially and psychologically. In this report, we focus on the approaches that involve optometrists in the investigation and management of patients with IN. Management includes the prescription of optical treatments, low-vision rehabilitation, and other interventions such as encouraging the use of the null zone and referral to support groups. Other treatments available via ophthalmologists are also briefly discussed in the article. Keywords: eye movements, visual acuity, reading performance, low vision, null zone, optometric investigation

Published
2017

87. Retinal Ganglion Cell Remodelling in Experimental Glaucoma.

Author

Back, Nathan, Cohen, Irun R., Kritchevsky, David, Lajtha, Abel, Paoletti, Rodolfo, Hollyfield, Joe G., Anderson, Robert E., LaVail, Matthew M., Morgan, James E., Datta, Amit V., Erichsen, Jonathan T., Albon, Julie, and Boulton, Michael E.

Abstract

Retinal ganglion cell (RGC) death is the key pathological event in glaucoma and the biological basis for the loss of vision. Although significant advances have been made in the medical and surgical treatment of glaucoma, the disease remains the most common cause, worldwide, of irreversible vision loss (Quigley, 1996). Our understanding of the role played by elevated intraocular pressure (IOP) in the initiation of glaucoma has recently been advanced by evidence from clinical trials that IOP levels within the normal range can influence the degree of retinal ganglion cell death (AGIS, 2000). For those patients with advanced glaucoma damage, a reduction in IOP, even within the normal range, can reduce the risk of progressive vision loss. [ABSTRACT FROM AUTHOR]

Published
2006
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98. Theta-Modulated Head Direction Cells in the Rat Anterior Thalamus.

Author

Tsanov, Marian, Chah, Ehsan, Vann, Seralynne D., Reilly, Richard B., Erichsen, Jonathan T., Aggleton, John P., and O'Mara, Shane M.

Subjects
ADNEXA oculi, CELL nuclei, THALAMUS, BRAIN
Abstract

A major tool in understanding how the brain processes information is the analysis of neuronal output at each hierarchical level along the pathway of signal propagation. Theta rhythm and head directionality are the two main signals found across all levels of Papez's circuit, which supports episodic memory formation. Here, we provide evidence that the functional interaction between both signals occurs at a subcortical level. We show that there is population of head direction cells (39%) in rat anteroventral thalamic nucleus that exhibit rhythmic spiking in the theta range. This class of units, termed HD-by-theta (head direction-by-theta) cells, discharged predominantly in spike trains at theta frequency (6-12 Hz). The highest degree of theta rhythmicity was evident when the animal was heading/facing in the preferred direction, expressed by the Gaussian peak of the directional tuning curve. The theta-rhythmic mode of spiking was closely related to the firing activity of local theta-bursting cells. We also found that 32% of anteroventral theta-bursting cells displayed a head-directional modulation of their spiking. This crossover between theta and head-directional signals indicates that anterior thalamus integrates information related to heading and movement, and may therefore actively modulate hippocampo-dencephalic information processing. [ABSTRACT FROM AUTHOR]

Published
2011
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99. Differential regulation of synaptic plasticity of the hippocampal and the hypothalamic inputs to the anterior thalamus.

Author

Tsanov, Marian, Vann, Seralynne D., Erichsen, Jonathan T., Wright, Nick, Aggleton, John P., and O'Mara, Shane M.

Abstract

The hippocampus projects to the anterior thalamic nuclei both directly and indirectly via the mammillary bodies, but little is known about the electrophysiological properties of these convergent pathways. Here we demonstrate, for the first time, the presence of long-term plasticity in anterior thalamic nuclei synapses in response to high- and low-frequency stimulation (LFS) in urethane-anesthetized rats. We compared the synaptic changes evoked via the direct vs. the indirect hippocampal pathways to the anterior thalamus, and found that long-term potentiation (LTP) of the thalamic field response is induced predominantly through the direct hippocampal projections. Furthermore, we have estimated that that long-term depression (LTD) can be induced only after stimulation of the indirect connections carried by the mammillothalamic tract. Interestingly, basal synaptic transmission mediated by the mammillothalamic tract undergoes use-dependent, BDNF-mediated potentiation, revealing a distinct form of plasticity specific to the diencephalic region. Our data indicate that the thalamus does not passively relay incoming information, but rather acts as a synaptic network, where the ability to integrate hippocampal and mammillary body inputs is dynamically modified as a result of previous activity in the circuit. The complementary properties of these two parallel pathways upon anterior thalamic activity reveal that they do not have duplicate functions. © 2009 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Published
2011
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