Psyc4130 1nd Edition Lecture 13 Outline of Last Lecture I Photoreceptors A Cones B Rods II Optic Disc III Theories of Coloring Code IV Visual Relay A Trichromatic B Opponent process C Retinex V dLGN VI Contraleteral Representation VII Primary Visual cortex Outline of Current Lecture VIII Opponent Process Theory IX Sensory Relay X Visual Relay XI dLGN XII Contralateral Representation XIII Primary Visual Cortex a Contralateral representation XIV Retinopic Organization XV V1 Lesions and Cortical Blindness XVI Characteristics of V1 Feature Detectors a Simple Cells b Complex Cells c Hypercomplex Cells XVII Characteristics of V1 a Spatial Frequency Detection b The Highs and Lows of Spatial Resolution XVIII Characteristics of V1 a Color Elements of V1 and V2 XIX Summary Current Lecture These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Opponent Process Theory o O P Theory posits the existence of red green and blue yellow color elements These elements can send a code to the brain from that small portion of their receptive field for either color but not at the same time o Fatiguing a color element by staring at an object reflecting that particular wavelength results in the opposite code being sent to the brain for a very brief period of time after the stimulus is removed This produces the afterimage Know trichromatic wont test on retinex Research with monkeys and neurological case studies with humans have confirmed that extrastriate area V4 is critical to color constancy V8 to interpret info or else color info is lost V8 most important Sensory Relay Environmental stimuli Neural relay getting signals to right part of the brain Visual Relay In thalamus Conscious retino geniculate striate Other o To superior colliculus o To pineal gland melatnonin o To SCN of hypothalamus zeitgebers Optic radiations V1 striate cortex dLGN Synapses of ganglion cell axons Preprocesses visual information goes through relay information first 6 major layers o P pathway retinal p cells parvo cellular very fines cells grainy cells like dust get specific info from cones break visual scene down into small pixels o M pathway retinal M cells magno cellular big receptive fields get primary info from rods motion detections Contralateral Representation Left occipital lobe gets info from right and vice versa except for smell o Decussation anatomical crossing over of half of the axons o Ipsilateral o Optic chiasma right info on left side of brain Primary Visual Cortex V1 Striate Cortex Midline along the banks of the calcarine fissure First cortical representation of visual signals originating in the retina Contralateral representation o Left visual field from both eyes projects exclusively to the RIGHT V1 and viceversa Retinotopic Organization The visual field is mapped on the retina upside down and backwards If V1 were cut out and flattened this retinal map corresponding to the contralateral visual field would be preserved That s to say there is a one to one correspondence between areas of the visual field mapped onto the retina and fields of neurons mapped onto V1 V1 Lesions and Cortical Blindness Due to retinotopic mapping damage to V1 wipes out any capacity for conscious vision in the corresponding visual field o Hemianopia o Quadrantanopia o Scotoma Characteristics of V1 Feature Detectors o Neural circuitry in V1 combines information from several sources i e signals arising in several ganglion cells in order to detect features larger than a single ganglion cell s receptive field o Three types of feature analytic cells have been characterized in V1 simple cells complex cells and hypercomplex cells Simple Cells o Simple cells have been demonstrated to respond most robustly to stimuli of specific orientations being presented in the middle of their receptive fields o Vertical diagonal horizontal responds maximally has object orientation preference i e might respond more to vertical lines than horizontal Complex Cells o Complex cells also respond most robustly to objects of a particular orientation but do not demonstrate an inhibitory surround both as active doesn t depend on orientation o Moving the object within the receptive field of a complex cell may actually increase the cell s rate of firing if moved perpendicular to the object s line of orientation Suggests a major role in MOTION DETECTION o Complex cells also respond equally to white objects against a black background or black objects against a white background Hypercomplex Cells o Respond to stimuli of a particular orientation but have inhibitory end regions o The apparent function is to very precisely detect the edges of objects Characteristics of V1 More recent research has shown that individual cells in V1 respond maximally to different spatial frequencies parallel gratings o SF variations in brightness in cycles per degree of visual angle The earlier research has suggested that neurons in V1 specialized in the detection of lines and edges but this is not the case Spatial Frequency Detection o The receptive fields of most neurons in V1 is large enough to include between 1 5 and 3 5 cycles of grating The Highs and Lows of Spatial Resolution o Fine details and sharp edges provide signals rich in high spatial frequency o Large areas of light and dark are represented by signals of low spatial frequency o Spatial filtering figure 6 27 Characteristics of V1 Neurons within V1 respond to retinal disparity the slight difference between where the image is cast on the right versus the left retina o Offset angular difference enables depth perception enhances it Enables stereopsis stereoscopic vision which is an important contributor to a rich sense of depth perception Color sensitive cells organized into cytochrome oxidase CO blobs Figure 6 28 Input is from P K layers of LGN This functional segregation continues as stripes into V2 Color Elements in V1 and V2 o Thick and thin stripes V2 stain heavily for CO whereas pale stripes do not Visual agnosia cant recognize objects Summary V1 neurons respond to several distinct features of visual stimuli including Object Orientation Movement Spatial Frequency Retinal Disparity Color