Psyc4130 1nd Edition Lecture 13 Outline of Last Lecture I. PhotoreceptorsA. ConesB. RodsII. Optic DiscIII.Theories of Coloring CodeIV.Visual RelayA.Trichromatic B.Opponent processC.Retinex V.dLGNVI. Contraleteral RepresentationVII. Primary Visual cortexOutline of Current Lecture VIII. Opponent Process TheoryIX. Sensory RelayX. Visual RelayXI. dLGNXII. Contralateral RepresentationXIII. Primary Visual Cortexa. Contralateral representationXIV. Retinopic OrganizationXV. V1 Lesions and Cortical BlindnessXVI. Characteristics of V1: Feature Detectorsa. Simple Cellsb. Complex Cellsc. Hypercomplex CellsXVII. Characteristics of V1a. Spatial Frequency Detectionb. The Highs and Lows of Spatial Resolution XVIII. Characteristics of V1a. Color Elements of V1 and V2XIX. SummaryCurrent LectureThese 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 Theoryo 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 timeo 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: melatnonino 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 layerso 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 pixelso 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 smello Decussation: anatomical crossing over of half of the axonso 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 representationo Left visual field (from both eyes) projects exclusively to the RIGHT V1 and vice-versa! 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 inthe corresponding visual field.o Hemianopiao Quadrantanopiao Scotoma Characteristics of V1: Feature Detectorso 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 Cellso 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 Cellso 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 Cellso Respond to stimuli of a particular orientation, but have inhibitory end regionso 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 Detectiono The receptive fields of most neurons in V1 is large enough to include between 1.5and 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 senseof 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 V2o 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-