Lecture17__0318_PSYC4041_24S_PDF.pdf

PSYC 4041: Cognitive Neuroscience Lecture 17: Higher-Level Vision & Visual Deficits 3/18/2024 Previously: Intro to the Visual System & Exam 2 ❖ WELCOME BACK! Today: Wednesday: Friday: Next week: Higher-Level Vision & Exam 2 score distributions Face Processing (Ch 7/9) & QALMRI review Attention (Ch 9...

PSYC 4041: Cognitive Neuroscience Lecture 17: Higher-Level Vision & Visual Deficits 3/18/2024 Previously: Intro to the Visual System & Exam 2 ❖ WELCOME BACK! Today: Wednesday: Friday: Next week: Higher-Level Vision & Exam 2 score distributions Face Processing (Ch 7/9) & QALMRI review Attention (Ch 9) & Exam 2 question review Attention (Ch 9) and Action (Ch 10) Today: The brain’s visual system — higher-level vision & visual deficits Exam 2: Score Distribution & Curve Score (40+5 bonus) → No Curve → Curved Grades: ❑ Median: ❑ Max: Frequency ❑ Min: 33 → 83% → 84% 33 → 83% → 84% 44 → 110% → 110% 17 → 43% → 49% Frequency ❑ Mean: F Exam 2 Score D C Exam 2 Curved Grade B A Exam 2: Score Distribution & Curve Score (40+5 bonus) → No Curve → Curved Grades: 33 → 33 → ❑ Mean: ❑ Median: 83% → 84% 83% → 84% Exam 2 Exam 2 Original Score → Curved Grade: ❑ If X ≥ 40: 𝑋 40 × 100 𝑋 ❑ If X < 40: 0.1 + ( × 0.9) × 100 40 ▪ Or replace ‘X’ & copy/paste into Google: (0.1+((x/40)*0.9))*100 Reminder: In-Class Participation Quizzes Average quiz scores: ❑ When attending class: 99.4% ❑ When not attending class: 0% → 15% + 5% extra credit Reminder: There will be at least 20 quizzes this semester. ❑ The best 15 scores count towards 15% of final grade. ❑ Any points above 15 will count as extra credit for final grade (up to 5%). ❑ Note: Correct answers are always posted with the Exam review material. Extra Credit: ❑ Quizzes will start counting towards extra credit after we have completed at least 15 quizzes. As of 3/18, we have completed 10 quizzes. ❑ Other extra credit sources: SONA-Systems & the Bonus 2/29 Lecture. ❑ 5% extra credit towards the final grade is an easy way to turn a B+ into an A! The Visual Brain: Vision is a constructive process Visual perception is not like a photograph — it is a constructive process with many stages and influences. Sensation: the effects of a stimulus on the sensory organs Perception: the elaboration and interpretation of that sensory stimulus by the brain Primary Visual Cortex Primary visual cortex (V1 / striate cortex) extracts basic info about visual input (e.g., edges, orientations, lines, length) ❑ This information is used in later stages to extract information about shape, color, movement, objects, etc. Visual Cortex: Hierarchy of receptive fields Receptive fields: different neurons (/brain areas) respond to particular locations of the visual field. ❑ The spatial scope of receptive fields is very specific for ganglion cells, neurons in V1, etc. ❑ Receptive field size generally increases along the visual processing pathway. Road Map: Higher-Level Vision & Visual Deficits Visual processing in extrastriate cortex & beyond: ▪ “WHAT” & “WHERE” processing streams ▪ Area V4 (color) ▪ Area V5/MT (motion) Functional neuroanatomy of object recognition ▪ 4-Stage Model of Object Recognition ▪ LOC: Perceptual grouping & shape processing ▪ Fusiform & IT Cortex: Object identity Visual Agnosias ▪ Deficits of object recognition Visual processing in extrastriate cortex and beyond “What” (ventral) and “where” (dorsal) pathways: ❑ Ventral: striate → extrastriate → (inferior) temporal lobe ▪ Processes stimulus features and identities; memory ❑ Dorsal: striate → extrastriate → parietal lobe ▪ Processes motion and spatial attention; action Road Map: Higher-Level Vision & Visual Deficits Visual processing in extrastriate cortex & beyond: ▪ “WHAT” & “WHERE” processing streams ▪ Area V4 (color) ▪ Area V5/MT (motion) Functional neuroanatomy of object recognition ▪ 4-Stage Model of Object Recognition ▪ LOC: Perceptual grouping & shape processing ▪ Fusiform & IT Cortex: Object identity Visual Agnosias ▪ Deficits of object recognition Extrastriate visual cortex: Area V4 & color Area V4 is the primary color center of the visual system Repeat for 30 seconds Repeat for 30 seconds Achromatopsia: damage causes visual perception to appear in greyscale Extrastriate visual cortex: Area V4 & color Extrastriate visual cortex: Area V4 & color Why does the brain need a color center when the retina has cone cells that respond to different wavelengths? ❑ Sensation vs perception: Color perception does *not* reflect absolute wavelength of visual input. Area V4 helps provide color constancy: the color of a surface/object is perceived as constant even when illuminated by different lighting conditions Extrastriate visual cortex: Area V4 & color Extrastriate visual cortex: Area V4 & color Extrastriate visual cortex: Area V4 & color Extrastriate visual cortex: Area V4 & color Why does the brain need a color center when the retina has cone cells that respond to different wavelengths? ❑ Sensation vs perception: Color perception does *not* reflect absolute wavelength of visual input. Color constancy: the color of a surface/object is perceived as constant even when illuminated by different lighting conditions (e.g. grass is perceived as green under both warm/orange light and cool/blue light) Area V4 takes into account illumination and lighting conditions across large area of visual space (large receptive fields) Extrastriate visual cortex: Area V4 & color Area V4 and color constancy: normally this works well, but can also lead to visual illusions such as “The Dress” Road Map: Higher-Level Vision & Visual Deficits Visual processing in extrastriate cortex & beyond: ▪ “WHAT” & “WHERE” processing streams ▪ Area V4 (color) ▪ Area V5/MT (motion) Functional neuroanatomy of object recognition ▪ 4-Stage Model of Object Recognition ▪ LOC: Perceptual grouping & shape processing ▪ Fusiform & IT Cortex: Object identity Visual Agnosias ▪ Deficits of object recognition Extrastriate visual cortex: Area V5/MT & motion Area V5/MT is the primary (visual) motion center in the brain ❑ Neurons respond to particular direction of motion ❑ Relatively larger receptive fields combine input from smaller receptive fields to detect motion Area V5/MT Area V4 Akinetopsia: damage causes failure to perceive *visual* motion Extrastriate visual cortex: Area V5/MT & motion Area V5/MT is the primary (visual) motion center in the brain ❑ Neurons respond to particular direction of motion ❑ Relatively larger receptive fields combine input from smaller receptive fields to detect motion Area V5/MT Area V4 Akinetopsia: damage causes failure to perceive *visual* motion Road Map: Higher-Level Vision & Visual Deficits Visual processing in extrastriate cortex & beyond: ▪ “WHAT” & “WHERE” processing streams ▪ Area V4 (color) ▪ Area V5/MT (motion) Functional neuroanatomy of object recognition ▪ 4-Stage Model of Object Recognition ▪ LOC: Perceptual grouping & shape processing ▪ Fusiform & IT Cortex: Object identity Visual Agnosias ▪ Deficits of object recognition Visual processing in extrastriate cortex and beyond “What” (ventral) and “where” (dorsal) pathways: Area V4 is the primary color center the visual system lobe ❑ Ventral: striate → extrastriate →of(inferior) temporal ▪ Processes stimulus features and identities; memory ❑ Dorsal: striate → extrastriate → parietal lobe ▪ Processes motion and spatial attention; action Visual processing in extrastriate cortex and beyond “What” (ventral) and “where” (dorsal) pathways: Area V4 isExtensive the primary color We center of theinfo visual system ❑ Note: cross-talk! use visual to shape our behavior Optic ataxia: inability to use vision to accurately guide action (without basic deficits of vision/movement, per se) Visual processing in extrastriate cortex and beyond Road Map: Higher-Level Vision & Visual Deficits Visual processing in extrastriate cortex & beyond: ▪ “WHAT” & “WHERE” processing streams ▪ Area V4 (color) ▪ Area V5/MT (motion) Functional neuroanatomy of object recognition ▪ 4-Stage Model of Object Recognition ▪ LOC: Perceptual grouping & shape processing ▪ Fusiform & IT Cortex: Object identity Visual Agnosias ▪ Deficits of object recognition 4-Stage Model of Object Recognition 1. Extract basic features (orientation, length, contrast, edges, etc.) ❑ Primary visual cortex & extrastriate cortex 2. Perceptual grouping (simple/complex shapes; foreground/background) ❑ Lateral Occipital Cortex (Area LOC) 3. Match visual perception to object (object constancy) ❑ Inferotemporal cortex (IT); fusiform gyrus 4. Object names/meaning (semantic information) ▪ Higher-order regions (Broca’s area, etc.) Fig 7.14 (p 158) Lateral Occipital Cortex & Perceptual Grouping Lateral Occipital Cortex is a key area for processing object shape ❑ Combines low-level components into high level-percepts Lateral Occipital Cortex & Perceptual Grouping Lateral Occipital Cortex is a key area for processing object shape ❑ Processing is typically size-independent but *not* viewpoint independent → processed as “same” shape → processed as “different” shape Lateral Occipital Cortex & Perceptual Grouping Lateral Occipital Cortex is a key area for processing object shape ❑ Combines low-level components into high level-percepts 4-Stage Model of Object Recognition 1. Extract basic features (orientation, length, contrast, edges, etc.) ❑ Primary visual cortex & extrastriate cortex 2. Perceptual grouping (simple/complex shapes; foreground/background) ❑ Lateral Occipital Cortex (Area LOC) 3. Match visual perception to object (object constancy) ❑ Inferotemporal cortex (IT); fusiform gyrus 4. Object names/meaning (semantic information) ▪ Higher-order regions (Broca’s area, etc.) Fig 7.14 (p 158) Fusiform Gyrus (& IT) → Object Constancy Fusiform gyrus (within inferotemporal cortex) is critical for providing object constancy (e.g. identifying whole objects) Fusiform Gyrus (& IT) → Object Constancy Object constancy is an understanding that the identity of an object remains the same independent of differences in viewing conditions (viewpoint, size, lighting, etc.) → processed as “same” object → processed as “different” object 4-Stage Model of Object Recognition 1. Extract basic features (orientation, length, contrast, edges, etc.) ❑ Primary visual cortex & extrastriate cortex 2. Perceptual grouping (simple/complex shapes; foreground/background) ❑ Lateral Occipital Cortex (Area LOC) 3. Match visual perception to object (object constancy) ❑ Inferotemporal cortex (IT); fusiform gyrus 4. Object names/meaning (semantic information) ▪ Higher-order regions (Broca’s area, etc.) Fig 7.14 (p 158) Functional neuroanatomy of object recognition → Primary visual cortex & extrastriate cortex → Lateral Occipital Cortex → Fusiform gyrus & inferotemporal cortex Fig 7.14 (p 158) Road Map: Higher-Level Vision & Visual Deficits Visual processing in extrastriate cortex & beyond: ▪ “WHAT” & “WHERE” processing streams ▪ Area V4 (color) ▪ Area V5/MT (motion) Functional neuroanatomy of object recognition ▪ 4-Stage Model of Object Recognition ▪ LOC: Perceptual grouping & shape processing ▪ Fusiform & IT Cortex: Object identity Visual Agnosias ▪ Deficits of object recognition Functional neuroanatomy of object recognition → Primary visual cortex & extrastriate cortex → Lateral Occipital Cortex → Fusiform gyrus & inferotemporal cortex Fig 7.14 (p 158) Visual Agnosias: deficits of object recognition Visual agnosia is a deficit in recognizing and understanding objects Deficit can arise from various underlying sources: ❑ Apperceptive agnosia is a deficit in object recognition due to impairment at the level of object perception Visual Agnosias: deficits of object recognition Visual Agnosias: deficits of object recognition Visual agnosia is a deficit in recognizing and understanding objects Deficit can arise from various underlying sources: ❑ Apperceptive agnosia is a deficit in object recognition due to impairment at the level of object perception ❑ Associative agnosia is a deficit in object recognition due to impairment at the level of knowledge/semantic memory Visual Agnosias: deficits of object recognition Patients with associative agnosia can copy visual information but do not understand it’s meaning Road Map: Higher-Level Vision & Visual Deficits Visual processing in extrastriate cortex & beyond: ▪ “WHAT” & “WHERE” processing streams ▪ Area V4 (color → color constancy) ▪ Area V5/MT (motion) Functional neuroanatomy of object recognition ▪ 4-Stage Model of Object Recognition ▪ LOC: Perceptual grouping & shape processing (shape constancy) ▪ Fusiform & IT Cortex: Object identity (object constancy) Visual Agnosias ▪ Deficits of object recognition Next class: QALMRI review, Face Processing, & Visual Attention