Class Notes (835,430)
Canada (509,186)
Psychology (7,782)
PSYB51H3 (314)
Lecture 6

PSYB51 lecture 6 .docx

8 Pages
86 Views
Unlock Document

Department
Psychology
Course
PSYB51H3
Professor
Matthias Neimier
Semester
Summer

Description
Lecture 6- PSYB51 What is the problem of univariance in colour vision? Please explain. What does it mean for vision based on a single type of colour- sensitive cone? How can the problem of univariance be solved?  The problem of univariance can be solved by having tricolor rods  Firing rate varies—universally based on: wave lengths, and intensity of the light. >cones will response differently depending on wavelength. 3 cones: Large = red Medium= green Short= blue  More cones= more richer colour vision Eye Movements
 – 6 muscles controlled by cranial nerves – Oculomotor control
 – Different eye movements
 – How do we achieve spatial constancy? Why talk about eye movements in a course on perception? - It could affect how we see the world - It is driven by attention - Motion -> quickly look at something ugly, dangerous, interesting, etc. - Move your eyes to points of interest so that you have a higher resolution - Eye movements are important to enhance our vision  Eye movements: six muscles are attached to each eye and are arranged in three pairs: – Inferior/superior/lateral/medial rectus – Inferior/superior oblique  Rectus muscle runs straight  Inferior rectus= bottom  Superior rectus= top  Boney hook= trochlea > As soon as you rotate your head more than 5degrees, your eyes counter rotate (you don’t really notice that- vision stays stable). > Passed 5 degrees, eyes make a quick motion, so a little disruption in vision (gaze is not stable) > Third dimension is rotation along sight > For each dimension of rotation, you would need 2 muscles > Muscles don’t do anything but pull Controlled by 3 cranial nerves  Extensive network
 – Frontal eye fields & parietal cortex => LOOK AT DIAGRAM – Superior colliculus: Structure in midbrain that plays important role in initiating and guiding eye movements – When stimulated with electrical signals, eye movements can be observed – Frontal eye field is the most important eye field in the cerebral cortex – Parietal cortex: somewhere around that area, there’s a region called lateral interpiratal area  Eye movements: – Smooth pursuit: Eyes move smoothly to follow 
 moving object – Saccade: Rapid movement of eyes that change fixation from one object or location to another -- Vergence eye movements (convergence and diversion movements): Type of eye movement in which two eyes move in opposite directions, done deliberately – Fixational eye movements, microsaccades (tiny versions of the saccades; it refreshes the eye) -> the eye never stays stable, it slides a bit  Function of smooth pursuit eye movements: keep object of interest stable and on the fovea.  Demonstration: Look at the background with the pencil moving across in the front you see that the eraser is clearer than the background  Why do we perceive the pencil to be in motion in the first case, but perceive the dot to be stationary in the second case? 
 – Because in one case there is an eye movement  Similar effects can be observed with saccadic eye movements  Function of saccades: move (rotate) fovea to object of interest, move as quickly as possible to reduce travel time during which vision is blurred.  Yarbus (1967): scanpaths reveal intentions and interests.  3-4 saccades/sec  False motion & retinal smear during saccade Why don’t we notice that?  Spatial constancy: Tricky problem of discriminating motion across the retina that is due to eye movements vs. object movements – Demonstrate this – Why does this happen? – Saccadic suppression (of vision, incl. motion): Reduction of visual sensitivity that occurs when one makes a saccadic eye movement; eliminates smear from retinal image motion during an eye movement  the vision starts shaking if you close one eye  When you push the eye, it moves – Remaining questions: > How does the brain know when to suppress? > Insufficient: displacements across saccades should result in apparent motion illusions (but doesn’t) > Botox was injected to the eye muscles to make it unusable. It appeared to him as if things were jumping around Compensation theory: Perceptual system receives information about the eye movement and discounts changes in retinal image that result from it (proposition) – Motor system sends motor command to eye muscles – A copy of that command (―efference copy‖, or colorily discharge) goes to an area of visual system that has been dubbed ―comparator‖ -> efference is anything that comes out of the brain -- Comparator compensates for image changes caused by the eye movement, inhibiting any attempts by other parts of the visual system to interpret changes as object motion [LOOK AT DIAGRAM] Space Perception and Binocular Vision  Euclidian geometry: Parallel lines remain parallel as they are extended in space – Objects maintain the same size and shape as they move around in space  they don’t shrink – Objects get bigger as they approach our eyes – Which sense is governed by Euclidian geometry?  Problem for vision: recover 3D info from 2D projections – Most depth cues can be derived from geometrical consequences of the projection  The two retinal images of a three-dimensional world are not the same! -> Parallax  Binocular disparity: The differences between the two retinal images of the same scene. It is the basis of stereopsis; a vivid perception of the three- dimensionality of the world that is not available with monocular vision.  Monocular depth cues vs. Binocular depth cues: One eye vs. two eyes  Binocular depth cues (from overlapping visual fields) provide: – Convergence – Stereopsis: is the impression of depth that is perceived when a scene is viewed with both eyes by someone with normal binocular vision – Ability of two eyes to see more of an object than one eye Monocular Cues to Three-Dimensional Space – Occlusion – Relative size
 – Position cues
 – Familiar size
 – Aerial perspective – Linear perspective – Motion cues  Occlusion: A cue to relative depth order when, for example, one object obstructs the view of part of another object – Nonmetrical depth cue: provides information about depth order but not magnitude. -> ex. we know there’s a square behind a circle; we just don’t know how far it is -- (Metrical depth cues: Provide quantitative information about distance)  Size and position cues: – Relative Size: A comparison of size between items without knowing the absolute size of either one (things UP on a picture means it’s closer to the horizon, and DOWN means closer to us) Size and position cues cont’d: – Texture Gradient: A depth cue based on the geometric fact that items of the same size form smaller images when they are farther away – Relative Height: Objects at different distances from the viewer on the ground plane will form images at different heights in the retinal image  The more remote parts in planes situated below the eye, appear higher (the projection EF of BC appears higher than the projection DE of AB). • Natural scene statistics. > There are two pictures of a smokey landscape. Th
More Less

Related notes for PSYB51H3

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit