Question

"When a visual stimulus is presented to us, our visual brain regions show two kinds of electrophysiological signals. One is fast and comes very soon (<100 ms) after the stimulus is shown, and can be traced to be coming from the retina through the thalamus. The other signal is slow and comes a bit later (>300 ms) after the stimulus, and can be traced to be coming from frontal and parietal regions. Disrupting these later signals that come from frontal and parietal regions however does disrupt vision. Why should this happen?"

I couldn't understand this question can you explain in details? I will rate. Thank you.

Answer 1

The human eye is being constantly exposed to a large number of visual stimuli all the time. The function of the retina is to only recieve these visual inputs and send them to the visual cortex. These signals are fast and comes as soon as the stimulus is shown (100 ms). Though it appears as if the eyes detects all stimuli, it only percieves selected few stimuli. This choice of what to see and what not to see comes as signals from the frontal and parietal regions. The frontal cortex is responsible for the cognitive functions. It picks out the visual stimuli that need to be seen. Hence, it helps in constructing the visual scene. Visual perception occurs on three stages.

• Selection of a part of the stimuli that we need to concentrate.
• Combination of these stimuli to form a meaningful image
• And the evaluation of this image to decide on what action has to be performed.

The frontal cortex is involved in this processing of the visual stimuli so that a meaningful action can be performed. The temporal lobe has the visual library which is constatly being updated. It helps to identify the image from past experiences.

The posterolateral part of the parietal lobe helps in visiospatial navigation and reasoning. It helps to distinguish two points and also in proprioception. It helps to locate an object in the field of vision.

Damage to these areas can affect visual perception. Frontal lesions can block out objects from the field of vision. Posterior parietal lesions results in optic ataxia, which can be explained as the inability to guide the hand towards an object.