Exm 1 SA - 52018 - Compatibility Mode - Saved to this PC Sign in Insert Draw Des

Question

Exm 1 SA - 52018 - Compatibility Mode - Saved to this PC Sign in Insert Draw Design Layout References Mailings Review ViewHelp Nitro Pro Tell me what you want to do File Home Share OFind Replace Select Editing Times New Roman Paste Emphasis Heading 1 Normal Strong Subtitle lipboard Forit Paragraph Styles , 3. You are seated in front of your computer (much like you are now!) and suddenly, a 2-inch, white bar of light moving at a 45o angle in a southeast direction comes across the screen. Describe how center-surround, simple, complex, and hypercomplex cells are involved in you seeing the bar of light. (8 pts) Page 1 of 2 228 words + 130% 12:26 PM Type here to search 2/9/2018

Explanation / Answer

The given beam of light will be perceived through the activation of the occipital cortex in the Brain which is the center for visual information in the human body. As the beam of light appears across the screen, this information will be picked by the retinal cells in the two eyes. The sensory input from the left eye and the right eye will then cross over at the Corpus Collosum leading to the transmission of information to the right and the left hemispheres respectively. The optic radiation leads from the LGN to primary visual cortex (V1). Then, the electrochemical messages will stimulate the cells of the Primary visual cortex or V-I which receives the maxium proportion of the visual information from the Lateral Geniculate Nucleus(LGN) and is the first processing area in the visual cortex. According to Huber and Wiesel, the primary visual area is composed of three types of cells: simple, complex and hyper-complex neurons. These three type of cells are orientation selective and direction selective. This means that the different respond differently to the change in the spatial position of the visual stimulus such the bar of light in the given example. Since the bar is moving at an angle of 45 degrees south -eastward across the screen, it would assume a diagonal orientation ( that is ) and it would evoke the largest number of action potentials in the neurons of the primary visual cortex. If the bar is elongated, then simple cells will respond the most to this stimulus and they will continue to fire action potential as the bar increases in length until a threshold is reached at which point there’s a plateau in excitation of the simple cells. Moreover, they have separate on-off regions that is if the information is present in the surrounding cells and not the center cells, then simple cells will not be stimulated by the visual information of the bar of light. Moreover, complex cells are not affected by the presentation of the input to the center center cells or the surround cells but function irrespective of this difference.In case of hyper complex cells, the response increases with increasing bar length up to some limit, but then as the bar is made longer the response is inhibited. This property is called end-stopping. Hyper complex cells would therefore be triggered more actively if the bar is of a shorter length. Hyper cells also do not have a separate on and off subregions for stimulation

Moreover, the three cells would also respond to the direction of movement of the bar of light. The neurons  respond strongly to oriented lines/bars/edges moving in a preferred direction such as, vertical lines moving to the right, but they do not respond to movements in opposite direction (e.g., vertical lines moving to the left). This function of direction selectivity influences simple, complex and hyper complex cells such that all three respond best to up-right motion but not at all to down-left motion.

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