Psyc4130 1nd Edition Lecture 14 Outline of Last Lecture II Opponent Process Theory III Sensory Relay IV Visual Relay V dLGN VI Contralateral Representation VII Primary Visual Cortex a Contralateral representation VIII Retinopic Organization IX V1 Lesions and Cortical Blindness X Characteristics of V1 Feature Detectors a Simple Cells b Complex Cells c Hypercomplex Cells XI Characteristics of V1 a Spatial Frequency Detection b The Highs and Lows of Spatial Resolution XII Characteristics of V1 a Color Elements of V1 and V2 XIII Summary Outline of Current Lecture I Extrastriate Cortex a V2 b Dorsal Stream Pathway c Ventral stream i V4 ii V8 iii LOC iv FFA v Prosopagnosia vi EBA vii PPA Current Lecture Extrastriate Cortex aka Visual Association cortex and Hierarchical processing 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 The response patterns of V1 are used as building blocks for creating a more complex visual analysis Humans Pretty Much Everybody Else Higher visual centers in the occipital and temporal lobes Humans have at least 30 different areas of the brain concerned with visual processing The functions of these regions tends to be highly specialized modular aka specificity more so than with most other perceptual functions Focal damage to specific discrete areas of extrastriate cortex can produce some very selective and fascinating changes in visual perception o V2 Receives signals from V1 Receptive fields are several times larger than in V1 because each neuron in V2 receives input from several V1 cells V2 gives rise to the dorsal and ventral visual pathways streams o Dorsal Stream Pathway Mostly M cell input know magnocellular big receptive cells fields lots of input form rods big areas of light dark contrast Important for skilled movements directed toward objects and for object localization Targeted focal damage within the dorsal stream can disrupt awareness of movement From V2 relays signals toward and into Posterior Parietal V5 ability to perceive constant and fluid streams of motion where and how pathway and Akinetopsia conscious awareness of fluid motion is gone Meanwhile the brains recognition pathway is uncompromised glass is half full wait no half empty oh crap When pouring water into a cup don t perceive glass filling up literally only see flashes and before they know it the cup has overflowed o Ventral Stream Important for detailed analysis of size shape color texture M and P cells contribute equally to the ventral visual stream From V2 toward and into Inferior Temporal V4 Color Constancy V8 Color perception fusiform gyrus Focal damage to V8 a posterior region of the inferior temporal cortex can cause cerebral achromatopsia cortical blindness vision without color Neurons in the more anterior regions of the inferior temporal cortex have HUGE receptive fields sometimes corresponding to nearly half of the contralateral visual field These cells continue to respond when objects move change size are placed against different background or are partially occluded Brain recognizes objects holistically i e can t see legs but know that they are there concerned with perception of the whole event object LO LOC Lateral Occipital Complex Object Recognition general visual agnosia inability to recognize something object i e can t tell you what mountain bike is can us it but can t describe it or say name can t recognize object Still within the occipital lobe headed down to temporal serves general role in object recognition The LOC responds to a wide variety of objects and shapes Damage to the LOC is likely to elicit visual agnosia deficits in visual perception in the absence of blindness Chapter 6 opening vignette FFA Aka fusiform face area Face recognition ability to recognize people by face People who have this can describe the face hair color eyes nose size but they can t pull it all together to say this is President Obamas face gestalt whole A functional imaging i e fMRI study by Golby and colleagues 2001 revealed that people s FFAs become more active when viewing faces of members of their own race than when viewing members of a different race Is FFA specific for face recognition As participants gained experience differentiating greebles they shift from part based to holistic processing At the same time fMRI studies revealed that participants come to engage the FFA while identifying greebles Prosopagnosia Patient can read can see color can describe objects can track object movement normally et cetera FACE BLINDNESS can t recognize who person is subconsciously break face down into geometric shape Patient cannot recognize people by face can t see larger picture only see geometric parts and face features Gestalt holistic processing fail brain sees triangle Prosopagnosia offers some of the best evidence to date of a domain specific modularity brain regions i e brain regions performing highly specific functions Recall the localization antilocalization debate in the history of neuroscience Of Greebles and FFA Data from the Greebles studies Gauthier and colleagues late 90 s were interpreted by many cognitive scientists to suggest that facial recognition wasn t as domainspecific as suggested by the case study data Object familiarity EBA PPA The EBA Extrastriate Body Area is found immediately posterior to the FFA with neuron fields partly overlapping It is so named because it responds more robustly to bodies or body parts than it does to faces feet legs arms overall body parts Also responds to faces Targeted focal damage within the ventral stream can disrupt recognition awareness Recognizing places natural manmade The Parahippocampal Place Area PPA is a region of limbic cortex specializing in the ability to recognize natural and hu manmade locations by their context D F a patient with profound damage to the LOC showed visual agnosia for objects but an intact recognition for scenes e g beaches forests markets cities et cetera Although she could recognize and name these locations when showed pictures of them she could not name specific items within the scenes e g trees sandcastles skyscrapers et cetera All of this being said we can never factor out the role of ATTENTION in visual perception