percept & cogn w2: Eyesight & Perception

Light

• electromagnetic energy

• Physical property is wavelength (colour)

• Intensity communicates brightness

• light interacts with the world

Perception

• acquisition and processing of stimulus

Refaction

• bending of light

• Lght changing directions when traveling from one medium to another

The human eye

• light refractd by the cornea And lens

• To focus image on the retina at the back of the eye

Ability to see close and far

Too long eye - far sighted

Too short eye - short sighted

Too much screen time and lack of outdoor time causes myopia. Too much reading and computer time

Increase in myopia over time since at the very least the 2000s.

90% of young ppl are short sighted in east vs 15-30% in europe

Reflection and absorption

• bright surfaces reflect a lot

• Wavelength of light determines colour

The eye-camera analogy

1. The eye-camera analogy is useful in

understanding how the eye works

2. Optics of the eye & of the camera both form an image

3. We might think of the retina of the eye and

the film in the camera as representing the

image?

Cornea and lens = camera lens

Pupil = aperture of camera

Cornea and lens

• refract light to form an image on the retina upside down

• Cornea has greater refractive power

Pupil and aperture

1. Our pupils dilate in low light levels

to let in more light

2. When photographing in low light

levels we can increase the camera

aperture to let in more ligh

Chromatic aberration

• when light does not manage to focus in one singular point, causing bleeding in colour

Aberration correction

• the use of both a concave and convex lens combined

The Yerkes-Dodson Law (arousal curve)

• sort of bell curve

• Height - performance

• Length - arousal

• Deep sleep - not much

• Altertness, interest, positive emotion - higher perf and arouse

• Optimal level of response and learning - a lot of both perf and arouse

• Increased emotional disturbance - high arousal, lowering perf

Might not be on exam

Receptor: rods and cones

Different types of camera films?

Rods

• operate in low light levels,

• high sensittivity.

• In periphery.

• Black and white.

• Low res

Cones

• need hihg light levels to function,

• low sensitivity.

• In fovea.

• Colour.

• High res

Macular degeneration

• Degeneration of central retina (macula). Blurred central focal vision me thinks

Cortical magnification

• fovea is over reresented in cortex

• High resolution

• Most sensitive parts are overrepretented in the motor cortex and somatosensory

• Some body parts take up more space in brain

Somatosensory plasticity

• if you glue together fingers for 24h, the representation of your fingers in your brain changes

Eye & camera neural factors

• eye - cones and rods

• Camera - colour film, high rest (cones), black/white film (rods)

Perception and knowledge

perception = the interpretation or inference. Unconscious process

Hermann von Helmholtz (1821-1894)

Unconscous inference - the way we fill in the gaps on our knowledge through perception

Richard Gregory

intelligent decision making from limited sensory evidence

Reasons why seeing is not like looking at photo

1. we do not see imperfections of visual

2. Illusions show that our brain ‘interprets’ the visual stimulus

3. We need attention to see

Rods and cones location

• rods: periphery

• Cones: fovea

Does it matter that the retinal image is upside down?

• Stratton’s Prism

• Worse inverting prisms for 8 days. Reported normal behaviour after first few days.

• Modern day: Niko Troje, Queens’ university

• We are not aware that the retinal imagine is upside down. In fact we can adapt to displacements and even to inversions of retinal images. This is different from simply loking at a photo

Ames Room (1950s)

• interdependence of perceived size

• The room is different, not the size of the men

Attention

• inattentional blindness - inability to see something fully obvious right before you bc attention is on something else

• Change blindness - cant tell diff between what is there right now and what was there a minute ago

• We only encode what is relevant for right then. Not other details. Main idea, not everything

Form perception

ability to visually perceive objects in the world in response to patterns of light that they caste on our retinas

Visual Agnosia

• apperceptive agnosia - cant regocnise objects, discrimate objecs, basic forms. Ex: the drawing of the elephant

• Associative agnosia - failure to link perception with stored knowledge. Ex: dont understan that drawing of a train is a train

• Prosopagnosia - face blindness. Cant recognize familiar faces, result of brain injury or congenital. May occur alone or a part of more general visual agnosias.

Bodamer (1947) Prosopagnosia

• defined by Bodamer

• Faces ”strangely flat, white with dark eyes as if on one plane. Flat oval plates” described by someone

Visual processing

1. Stage 1: Interpreting elements or parts (starts here in the occi)

2. Stage 2: Processing the whole

The visual pathway eye to brain

temporal retina —) optic nerve —) optic chiasm —) left side Of lateral geniculate nucleus —› primary visual cortex (occi)

Left visual field (LVF) —) left brain

Right visual field (RVF) —) right brain

Visual pathways within the cortex

• receiving area from vision is striate cortex in occipital lobe

• Then, dorsally to parietal cortex or ventrally to inferotemporal cortex

Dorsal

where pathway, parietal (spatial)

Ventral

what pathway, interotemporal (visual)

Structuralism

we see whole objects by combining elementary sensations

Gestalt

the whole is made of up its parts

Single unit recording

• intracellular recordings : recorder inside the cell itself. Damage the cell, not great. Nosier recordings

• Extracellular: single unit recording. Electrode placed outside of the cell.

Spike sorting

disentangle signal from recordings. See patterns, point out the outstanding wave forms. Wave form suggests different cells sometimes

Simple cells

feature detectors

Feature detection models - Selfridge (1959)

• image demon?

• Evidence for feature detection model: Find the Z - easy because surrounded by not similar shapes

Max Wertheimer

• gestalt man

• Looking at the elemental features, early visual processing

• Whole is bigger than the sum of its parts

Laws of grouping in gestalt

• proximity - elements close together are grouped together

• Similarity - elements similar in shape or size or colour are grouped

• Goood continuation - elements follow same direction or path are grouped together

• Closure - elements in a closed figure are grouped together - see a panda in random blobs, etc

• Common fate - moving in same direction and speed are grouped together

THESE WILL BE ON THE EXAM

Why do our brains use gestalt principles?

the brian doesnt like suspicious coincidences

Configural processing of faces and the thatcher illusion

• loss of configural processing may underlie some cases of prosopagnosia