Αντίληψη (2016) Όραση Μαρία Κουτρομάνου

Structure of the Eye: Iris The iris is similar to the diaphragm in a camera Your iris widens in dim light and narrows in bright light The f-number of your eye varies from f/2 (large opening) to f/8 (small opening) Compare this to the range of an average camera lens, which may have f-numbers from f/2.8 to f/22.

Structure of the Eye: Iris The range of intensities that your eye can respond to is a factor of The main function of the iris is not to control the intensity of light coming into your eye Main functions of iris – Reduce aberrations, sharpen image – Increase depth of field

Structure of the Eye: Cornea and Lens Cornea There are two lenses in your eye, the cornea and the eyelens. The cornea, the front surface of the eye, does most of the focusing in your eye The eyelens provides adjustable fine-tuning of the focus Eyelens

Structure of the Eye: Cornea and Lens air: n = 1 cornea: n ≈ 1.4 humors: n ≈ 1.3 eyelens: n ≈ 1.4 This is because the cornea-air surface has a large change in the index of refraction, so light bends a lot The power of the cornea lens is ~43 diopters (focal length 2.3 cm) The eyelens is surrounded by the humors, which have a very similar index of refraction as the lens itself.

The Eyelens: Accommodation The eyelens changes its focal length by changing its shape. Ligaments pull on the lens to change the amount of “bulge”

Eyelens: Accommodation Muscles contract, ligaments relax, more bulge, more bending power, shorter focal length Muscles relax, ligaments contract, less bulge, less bending power, longer focal length Ligaments Eyelens

How Your Eyelens Focuses Your eyelens has a small depth of field – You can't see something close and far with both objects in focus at the same time Hold out your thumb about a foot away from your eye – Then, alternately focus on thumb and me (right above your thumb) Note that you cannot see both me and your thumb sharply (in focus) at the same time – You focus on one or the other by changing the bulge of your eyelens

Κοντινά αντικείμενα  σύγκλιση ματιών Χρειάζεται διαστολή κόρης για να εστιαστεί η ακτίνα περισσότερο στη φοβία, αλλιώς θολή εικόνα Αλλαγή φακού: συστολή ακτινωτού σώματος  πιο στρογγυλός φακός Χαλαρό ακτινωτό σώμα  επίπεδος φακός  καλή όραση για μακρινά αντικείμενα Μυωπία: για μακρινά αντικείμενα ο φακός δεν είναι επίπεδος  σύγκλιση εικόνας πριν τον αμφιβληστροειδή (ενώ στο φυσιολογικό μάτι στον αμφιβληστροειδή) Υπερμετρωπία: εστίαση φωτινών ακτίνων μετά τον αμφιβληστροειδή (3:44-5:48)

less bulgy, longer f thumb is out of focus less bulgy, longer f professor is in focus more bulgy, shorter f thumb is in focus professor is out of focus

Γιατί ανεστραμμένο είδωλο στον αμφιβληστροειδή; -Διάθλαση φωτός από τον φακό αντιστροφή εικόνας στον εγκέφαλο Ένωση εικόνων από τα δύο μάτια  cheshire cat illusion: ανταγωνιστικές εικόνες στα 2 μάτια, μία στατική, μία με κίνηση, επικρατεί η κίνηση και «χάνουμε» το στατικό πρόσωπο που βλέπει το άλλο μάτι.

Rods & cones: 4 key differences between scotopic and photopic vision Contrast sensitivity Distribution of rods and cones Spectral sensitivity of rods and cones Sensitivity to light of rods and cones.

1. Rods are more sensitive than cones (x50) 2. There are more rods than cones (x10) 3. Ganglion cells have larger RFs for rods than cones (i.e. more post-receptoral summation)

1. Contrast sensitivity functions at three different light levels Spatial Frequency (cycles/mm on retina) Spatial frequency (cycles/degree) Sensitivity (1/threshold contrast)

2. Distribution of rods and cones visual eccentricity (deg) spatial density (cells/square mm) macula lutea cones rods retinal eccentricity (mm)

3. Spectral sensitivity curves for rod and cone vision Relative sensitivity Wavelength (nm)

Purkinje effect A shift in the colour appearance at dusk. Reds look darker, blues look brighter

Dark adaptation curves Low Log. light sensitivity High Time in dark (min) Cones Rods

Light and Dark Adaptation Light adaptation: Dark → light. Faster. Dark adaptation: Light →dark. Slow.

Υποδεκτικά πεδία στον αμφιβληστροειδή On-off, off-on υποδεκτικά πεδία αμφιβληστροειδή και για δίπολα και για γαγγλιακά κύτταρα: κέντρο ανταγωνισμός με περιφέρεια. Animation: /content/receptivefields.html