The Role of Parietal Cortex in Visual Memory

Introduction

As human beings live in a diverse environment, they own distinct senses, which enable them to live and interact with the world efficiently. All human beings’ actions are usually a replica of what their senses perceive (Olivers 37). Senses guide people in picking items from their surroundings depending on criteria. For instance, when one goes out shopping for attires, one can distinguish feminine clothes from masculine clothes. In a shopping mall, one can distinguish between the different types of clothes, depending on their shape and design. Let us say one wants to buy a pair of trouser. One will automatically be able to distinguish a feminine trouser from a masculine trouser through design, size, and shape. However, if one only employs the design to select a feminine trouser, one is likely to end up with male attire. Following the selection of the right item, one purchase. Hence, the claim that senses lead to action. This case demonstrates a connection between insight, knowledge, and deed. In the example, aspects of the item that can be seen direct the choice of an item that symbolizes the aim of an ensuing deed. This project examines the role of the parietal cortex in visual memory. Human beings can locate items in a visual sight naturally and fast. By forming a map of the exterior world that integrates up-bottom cognitive inputs and down-up sensory, this is easily achievable.

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Eyes Movement

A person is only able to visualize the environment through the fovea. Hence, human beings should be able to move fovea in different directions, so that they can acquire diverse information. This is possible through eye movements. The eye moves in a method that it is feasible to examine the target im with a high acuity, through foveating the item. Eyes movement to a novel position chiefly occurs by execution of a saccade. Saccades are abrupt, swift eye movements. It requires almost 100-300ms to start a saccade, that is, as of the moment when the presentation of a stimulus occurs till when the eye begins to move, and an extra 30-120ms to finish the saccade, depending on the visual angle that it crosses. It is possible to start saccades voluntarily, but when they begin, it becomes hard to change their course of motion and objective (Downing 12). This demonstrates that visual attention in the tangential region chooses the next position that the eyes move. Consequently, processing of the retinal image chiefly occurs amid the saccades, in the course of fixations which end after about 200-600ms (Hoffman 67). There also exist spontaneous eye activities, for instance, micro saccades, which retain fixation on steady items. Fixation eye movements take place as a gauge of return after a movement by the body or head. For instance, the ocular reflex aids in sustaining fixation in the course of a head movement by turning eyes in the reverse path of the head movement with just about a similar speed and velocity.

Saccade Target Selection

One should appreciate Saccade target selection in connection to the apparent fact that vision physically takes place in a constant series of fixations. The control of eye movements necessitates knowledge regarding what is where in the visual region (Milner 43). The characteristics of items result from their observable aspects. For instance, a person shopping sports port shoes will not only compare the shape but also the material of the shoes. Lone neurons in the visual structure symbolize the existence of definite aspects by the height of activation.

Various populations of neurons that all sorts of features trigger symbolize every position in the visual sphere. Topographic symbols exist all through the oculomotor and visual structures; adjacent neurons are likely to symbolize analogous visual field saccades or positions. Picking one from several stimuli in which to express gaze necessitates comparing stimulus features across the visual sphere. The subsistence of retinotopic maps of the visual sphere allows local relations to execute such associations. For instance, a lateral reserve network can remove the position of the most noticeable stimulus in the visual sphere. Creation of organizations accountable for making movements like the superior colliculus and FEF matches with this corresponding visual processing. A study by Hoffman reveals that “when the neurons at one location within the motor maps become sufficiently active, it produces a saccade” (67). Visual processing ensures that only a single site within a movement map becomes activated. This takes place when the neurons pointing the position of the target that one needs build up better activation as attenuation of the neurons responding to other positions occur.

Saccade target selection usually changes an originally ambiguous design of neural activation into a design that consistently pointto s one target place (Hoffman 67). Preceding knowledge of the probable target place or characteristics may lessen the ambiguity, and extra retinal indicators signifying such expectations can transform the receptiveness of afferent visual neurons. Activating the movement and identifying the measures of a saccade are corresponding but dissociable courses. Although there are several gaps in understanding, the queries to ask appear sensibly apparent. Since saccade target choice entails eye movement encoding and visual processing joint with mnemonic pressures, only constant experimental skill will unravel the diverse and erratic activities of individual neurons.

Visual Working Memory

Every day, people frequently employ their skills momentarily to store data up to completion of tasks. Working memory, which is the practice of keenly preserving pertinent information in the brain for some time, lies beneath this skill. One extremely significant notion of working memory is the multiple component models (Duncan and Humphreys 25). This model proposes two autonomous buffers for the storeroom of visuospatial and verbal information. In a recent translation, of the model an extra buffer that relates information across spheres to shape integral units of visual, verbal and spatial information exists. The central executive enables it to control information within and amid diverse buffers.

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Working memory is essential since visual information must be kept for using in future target choice, as seen in the case of buying sport shoes. Visual working memory offers a vital link amid perception and superior cognitive roles, making the active preservation of information regarding stimuli to be no more in sight. Studies show that constant action in higher-order parietal, infratemporal, prefrontal and lateral occipital regions backs visual protection (Duncan and Humphreys 27).

Since higher-order regions are short of the visual selectivity of initial sensory regions, it stays indistinct how viewers can retain precise visual aspects, for instance the course of a grating, with smallest delay in presentation over impediment f of several seconds. One suggestion is that sensory regions act to preserve fine-tuned characteristic information, but initial visual regions demonstrate little to no constant activity over lingering impediments.

The actuality that it is possible to recall a target site on the grounds of establishment in an attentional structure, and reticence in the oculomotor structure opens the likelihood that working memory errands arise via the conscription of brain systems that take part in roles that are sensory and that which relate to action. In the acute, there is the likelihood that working memory is simply the grounding to execute any deed ranging from verbal to oculomotor. In line with this embryonic property standpoint of working memory, the temporary preservation of spatial data is not inevitably the consequence of structures, for instance visuospatial scratch pad which may fail to exist in the prefrontal cortex, but comes from the competence that motor control and spatial attention presents.

The oculomotor action that associates with the site that one recalls in the SC outcomes in inhibition. Eyes coil away from this site and impediment of saccades in recurring to the site on inhibition occurs.

There are lots of relationships amid the working memory and spatial attention. Sudden onsets have the potential to incarcerate spatial attention in a distinctive manner. There exists proof that task-irrelevant arrivals can augment saccade potential. There seems to be a sturdy connection amid attention and visual working memory. Similarly, strong connection exists amid eye movements and spatial attention. Studies reveal that eyes naturally move to the site where there is attention, while the location of attention is at potential saccade goals.

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Eye Movement and Working Memory

Although it is feasible to direct attention to data that are already in the working memory, it is too feasible to direct attention to pertinent information that exists in the situation. Most studies demonstrate that the allotment of visual attention to places in visual space outcomes improvement in the dispensation of data that exist at the location of concentration on both neural and behavioral stage (Duncan and Humphreys 28). Conversely, controlled eye movements considerably spoil performance in the spatial imagery memory role, the inference being that they share processing power with spatial imagery. This is evident since eye movements occur during remembrance signifying an impact on programming and reclamation.

Current work by Hoffman points out that there is a close relation amid visual attention and working memory (69). He demonstrates that when the working memory serves as a storage location, there is ease of stimuli processing at the place of memory in relation to other places, similar to how attending to a site enhances the processing of data at that place. On the other hand, in case attention to sites of memorization becomes intermittent, the capacity to remember these sites will become spoilt. Research on working memory substantiates the belief that practice of spatial information alters early sensory regions and that an identical fronto-parietal network takes part in attention-associated activities.

Neural Processing of Visual Information for Saccade

So as, to formulate an eye movement to an object of desire, the brain must process visual information for it to choose a goal. Research on the neurophysiology of the macaque monkey gives proof for the survival of two practically different neural streams in the brain, which influence the processing of visual data. Psychological studies on persons with brain injury suggest that “the ventral stream starting from the primary visual cortex to the inferior temporal cortex influence perception, and that the dorsal stream starting from the primary visual cortex to the posterior parietal cortex influence action” (Downing 22). Other studies reveal that paths for oculomotor control and perception, in the motor organization of eye movements, overlap hugely, leading to momentous distribution of visual data (Downing 23). Additionally, the latest studies relate regions in the ventral stream with target choice of saccades (Barsalou 54). Hence, considerable incongruity exists regarding the extent to which the visual information accessible for perception is usable for saccadic targeting. In case disconnect ventral and dorsal visual pathways direct perception and eye movements, then diverse neural regions will direct perceptual and saccadic choices. These diverse neural regions will probably execute diverse computations and employ neurons with diverse receptive spheres. If this happens, the depictions of visual saccades target and the target for perception will vary. Conversely, if the distribution of information occurs crosswise from the ventral streams and dorsal and perceptual and saccadic, it will follow that the processing and receptive spheres that carry perceptual and saccadic choices will be identical.

Neural Processing of Visual Working Memory

After examining the neural processing of visual information for saccades, we can examine the brain regions that have connections with the visual working memory. Working memory is the practice of dynamically maintaining a symbol of information for a concise duration of time so that it is accessible for use. In monkeys, visual working memory entails rigorous action of a well-spread neural structure, with anterior regions in the prefrontal cortex and posterior regions in visual cortex (Lewald 250). Ventral stream regions in the visual cortex particularly take part in object vision, while dorsal stream regions take part specifically in spatial vision. This sphere specificity seems to expand further into the prefrontal cortex, with dorsolateral regions specially taking part in the working memory for spatial sites and ventrolateral regions especially taking part in the working memory for items. The arrangement of the wide-spread neural structure for working memory in monkeys seems to exist in humans, although several disparities exist amid the two classes. In persons, weighing against monkeys, regions for spatial vision in the dorsal stream boast a better site in the parietal cortex but regions for object vision in the ventral stream boast an inferior site in the temporal cortex (Lewald 251).

Dislocation of both sites of visual regions away from the posterior perisylvian cortex has associations with the surfacing of speech in the process of brain development. A study by Lewald reveals that while locations for regions specific for object working memory in monkeys and persons are equally in ventrolateral prefrontal cortex, those specific for spatial working memory take up a higher and posterior site in the dorsal prefrontal cortex in humans than in monkeys (259). For the posterior cortex, this dislocation in the frontal cortex has associations with the surfacing of new regions to serve human cognitive skills.

Parietal Cortex

The location of the parietal cortex is in between where vision ends and where motor control begins. The posterior area (PPC) comprises of numerous sub-areas, with conflicting outputs and inputs that take part in diverse roles (Lewald 256). The posterior parietal cortex (PPC) accepts several inputs including aural, limbic, visual, somaesthetic and motor. Parietal cortex has strong relations with cingulate gyrus, the frontal cortex, and the motor structure (Farah 16). When stroke attacks the right-side PPC, a weird condition whereby the patient appears to be oblivious of the left region of space occurs. At times, patients fail to recognize their environment on that area, and other times their individual bodies appear strange to them. Hence, it is evident that the PPC plays a role in spatial processing. Additional areas whereby the parietal cortex has roles to play include: visuomotor alteration, attention, motor command creation, multimodal incorporation and perception ((Lewald 256).

Neuroscientific methods like transcranial magnetic stimulation and MRI imaging propose that, the posterior parietal cortex (PPC) that seems to be vital for the direction of eye movements and spatial processing may as well have an outer function in visual attention. PPC impairment owing to stroke habitually results to the clinical disorder of neglect, whereby patients appear incapable of attending to actions in the contralesional hemifield (Godijn 115). One hypothesis can be that the lateral intraparietal area (LIP) of posterior parietal cortex functions as a precedence map, whereby the creation of eye movements of the highest activity takes place. The location of LIP is at the lateral rear of the intraparietal sulcus, and it seems to have a role in saccadic eye movements (Godijn 117).

Area LIP displays a much sturdy projection than that occuring from area 7a to the superior colliculus and the frontal eye spheres, the two constructions that take part in the creation of saccades. LIP is the receiver of inputs from a number of extrastriate cortical regions, taking in the middle temporal area (MT), a cortical sphere drawn in in visual movement processing ((Lewald 256)).

Transcranial Magnetic Stimulation (TMS)

Since people make three to five saccades in each second, information that develops across several fixations should aid in constructing an awareness of a cohesive visual globe, by the name transsaccadic integration (Walsh 147). So that, the transsaccadic integration of visual information can generate a constant depiction of the visual environment, the visual structure has to preserve visual data athwart saccades. This course of preserving visual data athwart saccades is transsaccadic memory. Studies reveal that transsaccadic memory has a faculty of three to four objects, analogous to visual working memory. Nevertheless, transsaccadic memory entails extra computational hassles that the visual system has to work out, which differentiates it from visual working memory, for instance the self-centered actions of saccade metrics on recording spatial information.

It appears possible that transsaccadic memory and perception would engage both the dorsal stream that ends in the posterior parietal cortex (PPC) and the ventral stream of vision, which ends in the temporal cortex and seems to mediate recognition. The subject of transsaccadic integration hence becomes equal to the broad query of how incorporation of data from these two streams occurs. One option is that it corresponds via lateral links. A different option is that data from both streams unites in the frontal cortex.

One can hypothesize that the feeding of data from the dorsal and ventral streams takes place rearwards via re-entrant paths, which normally undergo integration in initial visual spheres. Although the PPC may be an element of a cortical network for spatial functioning, the demonstration of its participation in transsaccadic memory of visual aspects is yet to come. Several studies reveal that LIP takes part in the direction of saccadic eye movements and the incorporation of extra-retina and retinal pointers. Furthermore, LIP takes part in the spatial renewing of object locations and saccade aims in eye movements, a practice given the name remapping.

Transcranial magnetic stimulation (TMS) has its foundation on Faraday’s ideology of electromagnetic generation (Pascual-Leone n. p.). A pulse of current streaming via a coil of wire produces a magnetic field (Pascual-Leone n. p.). If the level, of this magnetic field changes in time, then it will stimulate a secondary current in any close conductor. The rate of alteration of the field determines the size of the current stimulated. In TMS study, the invigorating coil seizes over a subject’s head and as a short pulsation of current transmits via it, and a magnetic field generates that pass all the way through the subject’s scalp and skull with insignificant decrease (Olivers 1246). This phase-dependent magnetic field stimulates a current in the subject’s mind, and this stimulates the neural tissue (Pascual-Leone n. p.). When applied practically at a sequence of pulses at rates of up to 50 Hz, it acquires the name recurring TMS, or rTMS.

A variation of TMS recurring transcranial magnetic stimulation (rTMS), is experienced as a healing instrument for a variety of neurological and psychiatric disorder counting migraines, Parkinson’s disease, tinnitus, strokes, dystonia, depression and auditory hallucination.

The medial parieto-occipital cortex is a mid-swelling in the dorsomedial image stream. Area V6 receives shape and activity in sequence straight from V1. V6A elaborate illustration information such as form, activity and room appropriate for the power of mutually attaining and acquisitive activities. In conclusion, V6A is jointly relates with the dorsal premotor cortex arm activities. The intraparietal sulcus (IPS) contains a sequence of functionally separate sub regions that are intensively investigated by means of mutually distinct cell neurophysiology in primates and human functional neuroimaging. Its main functions relate to perceptual-motor harmonization (for directing eye activities and accomplishment) and visual attention.

Parieto-occipital cortex exhibits superior reactions to entity pairs described as relating than when they are not. The occipital cortex is transformed by the intraparietal sulcus (IPS), which occasionally exhibits analogous pattern of reactions with the cortex.

References

Barsalou, Laura. “Grounded Cognition.” Annual Review of Psychology 59 (2008): 617-645.

Downing, Patrick. “Competition in Visual Working Memory for Control of Search.” Visual Cognition 11 (2004): 689–703.

Duncan, Jacque and Humphreys Schuman. “Visual Search and Stimulus Similarity. “Psychological Review 96(1984): 433-458.

Farah, Morah. “Psychophysical Evidence for Shared Representational Medium for Mental Images and Percepts.” Journal of Experimental Psychology 114(1999): 91-103

Godijn, Theeuwes. “Programming of Endogenous and Exogenous Saccades: Evidence for a Competitive Integration Model.” Journal of Experimental Psychology 28 (2003): 1039-1054.

Hoffman, Jared. “Saccadic Eye Movements and Visual Selective Attention.” Perception and Psychophysics 57 (1995): 787-795.

Lewald, Foltys. “Role of the Posterior Parietal Cortex in Spatial Vision.” Journal of Neuroscience 22 7(2002):1–5

Milner, A. The Visual Brain in Action. New York: Oxford University Press, 2006.

Olivers, Meijer. “Feature-Based Memory-Driven Attentional Capture: Visual Working Memory Content Affects Visual Attention.” Journal of Experimental Psychology: Human Perception and Performance 32 (1999):1243-1265

Pascual-Leone, Alvaro, Vincent Walsh and John Rothwell. Transcranial Magnetic Stimulation in Cognitive Neuroscience. Web. 2011

Walsh, Vincent. Transcranial Magnetic Stimulation: A Neurochronometrics of Mind. Cambridge: MIT Press, 2005.

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