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None of the participants reported phosphenes during the experiment. Ashbridge et al. This specific time window was used in order to allow sufficient time for the generation of the mental image and to avoid a close temporal proximity of the TMS pulse train with the test cue.

The neural basis of spatial vision losses in the dysfunctional visual system.

At the end of the experiment, participants were asked to fill a questionnaire assessing their cognitive strategies during the experiment and ensure that instructions were followed. On the basis of this questionnaire, five participants were excluded from the data analysis.

Two participants were excluded because they had not used imagery when required. Three participants reported using the same maintenance process across all sessions e. None of the other main effects or interactions were significant.

To understand the nature of these effects, we carried out post-hoc comparisons. To investigate whether baseline performance i. However, no other main effect or interaction was found highest p -value 0.

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In contrast, TMS had no impact on sensitivity in the concurrent condition. The baseline performance level of imagery and VSTM did not differ, and was not modulated by the task i. The Error bars indicate SDs from which between-subjects variance has been removed Loftus and Masson, None of the interactions were significant.

None of the other interactions were significant. No such effect was found for imagery. The aim of this study was to examine whether the neural bases of VSTM and imagery are dissociable in the early visual cortex. A dissociation between VSTM and imagery was present in the reaction times.

For example, phosphene studies have shown TMS to facilitate the features contained in both imagery Sparing et al.

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However, the results of this study beg the question of why the effects on sensitivity and reaction times were qualitatively very different. It is generally assumed that the impact of TMS on these two measures occurs via the same mechanism. TMS is believed to act by indiscriminately activating neurons in the targeted region, thereby adding noise to the highly organized pattern of neural activity associated with perceptual processes see e. Walsh et al.

This can slow down reaction times, as more time is needed to accumulate the necessary level of evidence required for the discrimination judgment, due to the increased amount of noise. Induction of noise can also reduce sensitivity by reducing the quality of the sensory representation on which the discrimination judgment is based. Of these two measures, reaction times are generally more sensitive to TMS-induced disruption, possibly because even small amounts of noise can slow down evidence accumulation, whereas the sensory signal might have sufficient redundancy to deal with low noise levels Walsh et al.

The neural basis of spatial vision losses in the dysfunctional visual system

In this view, whenever accuracy is reduced, an effect on reaction times should also be observed, as the latter is more susceptible to disruption. To account for these results, it thus appears to be necessary to postulate that reaction times and sensitivity reflect distinct neural processes. What might these be? The key difference between items in VSTM and imagery is that the latter are already in the conscious domain Logie, , and thus do not require a separate stage of retrieval before they can be compared with the test cue.

In contrast, VSTM content needs to be consciously accessed for the discrimination task to be performed. It might be that for the latter, TMS had no impact in the imagery task because the mental image is already in the conscious domain and therefore such retrieval is not needed. However, VSTM content needs to be re-accessed in order for the discrimination task to be performed.

In this study VSTM maintenance did not entail efforts in regenerating an image of the cue once the iconic memory had faded. For this reason, the VSTM task but not the imagery task involves a separate stage of retrieval of accessing memory content and the ease of this process might have been affected by TMS. One possibility is that, during simultaneous VSTM and imagery, the underlying memory trace on which both items are based is stronger.

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It could be that with sufficiently strong representation, TMS is no longer able to enhance it further. Another possibility is that VSTM and imagery involve different representations and that during the maintenance period, these interact. This interaction could be bidirectional, with the mental image itself strengthening the underlying VSTM trace.

In this view, VSTM and imagery would be based on partly distinct representations. In summary, the key finding of the present study is that TMS had a differential impact on the reaction times of VSTM and imagery, dissociating these processes at the level of the early visual cortex. Logie, , but also at the level of the visual representations.

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ES is supported by a scholarship from the Kordelin Foundation. Europe PMC requires Javascript to function effectively. Recent Activity. In the "alone" condition, participants were asked to engage either in VSTM or imagery, whereas in the "concurrent" condition, each trial required both VSTM maintenance and imagery simultaneously.

The snippet could not be located in the article text. This may be because the snippet appears in a figure legend, contains special characters or spans different sections of the article. PMID: Elyana Saad: moc. Abstract Visual short-term memory VSTM and visual imagery are believed to involve overlapping neuronal representations in the early visual cortex. Materials and methods 2. Participants 23 participants 9 females; mean age 25 years with normal vision participated in the experiment.

Stimuli Stimuli and task were controlled by E-prime v2. Experimental sessions 3 types of blocks were run: 1. VSTM alone-assessment of memory for the original memory cue. In these blocks, participants were instructed to hold the cue contrast in memory, without engaging in imagery throughout the trial.

In other words, participants were not required to maintain a conscious mental image throughout the delay period in other words, phenomenal experience of the qualia of the memory content was not required during maintenance. At the end of the trial, they were required to judge whether the test cue was of lower or higher contrast than the original memory cue. Imagery alone; assessment of accuracy of the conscious mental image. In these blocks, participants were asked to maintain conscious mental image of the original imagery cue throughout the delay period, where the mental image contrast was compared to the test cue.

In other words, the contrast judgment was based on an online inspection of the mental image. In these blocks, participants were informed at the end of the maintenance period whether memory or imagery would be assessed. Open in a separate window. Questionnaire assessing task strategy At the end of the experiment, participants were asked to fill a questionnaire assessing their cognitive strategies during the experiment and ensure that instructions were followed. Overall effects of TMS on reaction times Fig.

Discussion The aim of this study was to examine whether the neural bases of VSTM and imagery are dissociable in the early visual cortex. Conflict of Interest The authors declare no competing financial interests. Acknowledgments ES is supported by a scholarship from the Kordelin Foundation. References Albers A. Shared representations for working memory and mental imagery in early visual cortex.


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He is a founding member of the Israeli-Palestinian Science Organization, a nonprofit alliance established in to support collaborative research between scientists to promote positive interactions between the two communities. Wiesel received his medical degree from the Karolinska Institute in Stockholm , and then taught in the Institute's department of physiology and worked in the child psychiatry unit of the Karolinska Hospital. He began a fellowship in ophthalmology at Johns Hopkins University Medical School in and became an assistant professor there in The following year he became an instructor in pharmacology at Harvard Medical School, beginning a year career with the university; he became professor in the new department of neurobiology in and its chair in During his term as president, he recruited 16 new faculty members, established six interdisciplinary research centers, and formed the University's collaborative relationship with the Aaron Diamond AIDS Research Center, of which he was chairman.

He is currently emeritus at Rockefeller and a visiting professor at the Karolinska Institute, and shares his time between New York and Stockholm.