Pemrosesan Informasi Visual di Otak PDF

Pemrosesan Informasi Visual di Otak  The rods and cones of the retina make synapses with horizontal cells and bipolar cells horizontal cells make inhibitory contact onto bipolar cells  The optic nerves from the two eyes meet at the optic chiasm half of the axons from each eye cross...

Pemrosesan Informasi Visual di Otak  The rods and cones of the retina make synapses with horizontal cells and bipolar cells horizontal cells make inhibitory contact onto bipolar cells  The optic nerves from the two eyes meet at the optic chiasm half of the axons from each eye cross to the opposite side of the brain Most ganglion cell axons go to the lateral geniculate nucleus, part of the thalamus. Pemrosesan di retina Lateral inhibition is the retina’s way of sharpening contrasts to emphasize the borders of objects. The receptors send messages to excite nearby bipolar cells and also send messages to horizontal cells that slightly inhibit those bipolar cells and the neighbors to their sides heighten the contrast between an illuminated area and its darker surround Receptive Fields Each cell in the visual system of the brain has a receptive field, an area in visual space that excites or inhibits it. One or more receptors connect to a bipolar cell, with a receptive field that is the sum of the receptive fields of all those rods or cones connected to it. Several bipolar cells report to a ganglion cell, which therefore has a still larger receptive field A ganglion cell has a receptive field consisting of a circular center and an antagonistic doughnut-shaped surround. That is, the receptive field might be excited by light in the center and inhibited by light in the surround, or the opposite Receptive Fields the visual system analyzes information in many ways from the start Axons from the ganglion cells form the optic nerve Most of the axons go to the lateral geniculate nucleus of the thalamus Cells of the lateral geniculate have receptive fields that resemble those of the ganglion cells After the information reaches the cerebral cortex, the receptive fields become more complicated. Primary Visual Cortex Information from the lateral geniculate nucleus of the thalamus goes to the primary visual cortex in the occipital cortex, also known as area V1 or the striate cortex People with damage to area V1 report no conscious vision, no visual imagery, and no visual images in their dreams In contrast, adults who lose vision because of eye damage continue to have visual imagery and visual dreams. Simple and Complex Receptive Fields Hubel and Wiesel distinguished several types of cells in the visual cortex. A simple cell has a receptive field with fixed excitatory and inhibitory zones. The more light shines in the excitatory zone, the more the cell responds. The more light shines in the inhibitory zone, the less the cell responds.  complex cells, located in areas V1 and V2, do not respond to the exact location of a stimulus. A complex cell responds to a pattern of light in a particular orientation (e.g., a vertical bar) anywhere within its large receptive field A cell that responds to a stimulus in only one location is a simple cell. One that responds equally throughout a large area is a complex cell  End-stopped/hypercomplex, cells resemble complex cells with one exception: An end-stopped cell has a strong inhibitory area at one end of its bar-shaped receptive field. Columnar Organization of the Visual Cortex Cells with similar properties group together in the visual cortex in columns perpendicular to the surface > cells within a given column respond best to lines of a single orientation Development of the Visual Cortex If an experimenter sutures one eyelid shut for a sensitive period, when experiences have a kitten’s first 4 to 6 weeks of life, synapses in the particularly strong and enduring influence visual cortex gradually become unresponsive to input from the deprived eye. After the deprived eye is opened, the kitten does not respond to it. Cortical plasticity is greatest in early life, but it never ends. in adults, after an eye deprived of vision is reopened, cells gradually return to their previous levels of responsiveness If both eyes stayed shut for the first few weeks the cortical responses start to become sluggish and lose their well-defined receptive fields. Eventually, the visual cortex starts responding to auditory and touch stimuli instead. Parallel Processing in the Visual Cortex What and Where Pathway Arus Ventral : “what” (mengidentifikasi dan mengenali suatu objek) Arus Dorsal : “where”/”how” (visually guided movement) Kerusakan pada salah satu (Ventral/Dorsal) juga memengaruhi bagian lainnya. Contoh: pasien DF mengalami kerusakan visual cortex dan temporal cortex (tidak dapat menyebutkan benda yg dilihat, tdk bisa mengenali wajah, tdk bisa membedakan bentuk benda, tapi bisa memasukkan amplop dg arah yg benar) Contoh: pasien JS mengalami kerusakan lobus temporal (tdk dpt menyebutkan lokasi benda, tapi bisa mengambil benda tsb)  The Dorsal and Ventral Streams Visual information moves along the dorsal and ventral streams to distinct higher- order visual areas. The dorsal stream processes the object location, features that tell us “where” it is. The ventral stream processes details of its color and shape, features that describe “what” it is. Principles of Behavioral Neuroscience, 1e Fig 3-22 ARUS VENTRAL Melalui korteks temporal Identifikasi dan mengenali objek Kerusakan pada area ini menyebabkan gangguan pengenalan objek ANALISIS DETAIL BENTUK Informasi visual mulai dari sel sederhana menuju ke sel kompleks lalu ke area otak yang lebih spesifik di korteks visual primer (v1) Di korteks visual sekunder (v2) terjadi spesialisasi sel Beberapa sel memfokuskan untuk merespon hanya pada informasi tertentu (lingkaran, garis tertentu) Walaupun banyak sel yang tetap merespon semua informasi ANALISIS DETAIL BENTUK Inferotemporal cortex Merespon objek yang bermakna Kerusakan pada bagian ini dapat menyebabkan visual agnosia Yaitu seseorang dapat mendeskripsikan suatu benda tetapi tidak dapat mengenali apa benda itu Sebagai contoh, pasien diperlihatkan stetoskop, dia akan mengenali benda tersebut sebagai tali kabel panjang dengan ujung berbentuk bulat, bukan stetoskop ANALISIS DETAIL BENTUK Recognizing Faces Area otak yang berperan: amygdala, face area occipital, dan beberapa bagian temporal cortex seperti fusiform gyrus Face area occipital merespon bagian wajah seperti mulut dan mata Fusiform gyrus merespon aspek kompleks dari wajah secara keseluruhan seperti menentukan Prosopagnosia= gangguan pada kemampuan dalam jenis kelamin mengenali wajah (Tetap dapat membaca, tetap dapat mengenali ciri- ciri wajah per-bagian, tetapi Fusiform gyrus juga memungkinkan kita untuk mengenali wajah tidak dapat mengenali wajah siapa itu secara seseorang dari berbagai sudut dan keseluruhan). mengenali gambar wajah seseorang Prosopagnosia “Thus, on several occasions I have apologized for almost bumping into a large bearded man, only to realize that the large bearded man was myself in a mirror. The opposite situation once occurred at a restaurant. Sitting at a sidewalk table, I turned toward the restaurant window and began grooming my beard, as I often do. I then realized that what I had taken to be my reflection was not grooming himself but looking at me oddly” - Oliver Sacks https://www.newyorker.com/magazine/2 010/08/30/face-blind PERSEPSI WARNA Area otak yang khususnya penting dalam persepsi warna ialah V4 Warna yang tampak pada sebuah objek tidak hanya dipengaruhi oleh cahaya yang terpantul dari objek tersebut, tetapi juga dari bagaimana objek tersebut menyandingkan dirinya dengan objek disekitarnya Respon sel V4 terhadap warna sesuai dengan warna yang di perceived dalam konteks keseluruhan sebuah objek Kerusakan pada area V4 menyebabkan hilangnya color constancy (bukan colorblind) Color constancy= kemampuan untuk mengenali warna yang tetap sama pada suatu objek walaupun pencahayaan sekitarnya berubah warna ARUS DORSAL Melalui korteks parietal Berperan dalam pergerakan yang dipandu visual Kerusakan pada bagian ini dapat menyebabkan gangguan pada koordinasi visual dan organ gerak Mereka dapat mengingat bentuk sebuah objek tetapi tidak dapat mengingat bagaimana objek itu diletakkan di sebuah ruangan PERSEPSI GERAKAN Middle temporal cortex Dua area yang penting dalam persepsi gerakan ialah middle temporal cortex (MT) atau (V5) dan medial superior temporal cortex (MST) yang menerima input terutama dari magnocellular path MT secara selektif merespon sesuatu yang bergerak pada kecepatan tertentu dan pada arah tertentu MT mendeteksi akselerasi, deselerasi, dan gerakan dalam tiga dimensi MT juga merespon pada gambar yang menyiratkan gerakan seperti foto orang berlari MST merespon stimulus yang lebih kompleks seperti ekspansi, kontraksi, dan rotasi Sederhananya, MT dan MST membantumu membedakan antara sesuatu yang diakibatkan pergerakan mata atau akibat pergerakan objek PERSEPSI GERAKAN Motion Blindness (Akinetopsia) Adalah gangguan pada kemampuan dalam melihat pergerakan (arah gerakan, kecepatan, dll) yang https://youtu.be/B47Js1MtT4w? disebabkan kerusakan pada area mt dan mst si=wQf4pDwCji8I1z02 Penderita gangguan ini dapat diilustrasikan sebagai berikut: dia melihat mobil dari kejauhan dalam posisi diam, tetapi ketika dia mau menyeberang, mobil tersebut sudah ada didekatnya Ada gangguan lain yang berkebalikan dari motion blindness yaitu mereka melihat pergerakan objek tetapi tidak bisa melihat objek tersebut Motion blindness lebih susah untuk dibayangkan, tidak seperti color blindness Kalat, J.W. (2019), Biological Psychology (13th edition), Boston, MA: Cengage Learning Horvitz, J. C., & Jacobs, B. L. (2022). Principles of Behavioral Neuroscience. Cambridge: Cambridge University Press.