Exam 2

Ace this b*tch

Visual pathway order

Visual pathway order

1. Retina

2. Optic Nerve

3. Optic chiasm - electrical signals crisscross

4. Lateral Geniculate Nucleus (LGN) - thalamus is relay station (pass on info)

5. Occipital lobe - cerebral cortex, contains visual receiving area, V1, Striate cortex

Lateral Geniculate Nucleus (LGN)

• Receives 90% of light info from optic nerve

• Other 10% goes to Superior Colliculus (controls eye movement)

• Receives feedback from Striate Cortex

• Transmits info to dorsal (where) & ventral (what) streams

Striate cortex

V1/Visual Receiving Area/Primary Visual Cortex (Location: Occipital lobe)

Receptive fields are side-by-side

Simple cortical cells

Excitatory/Inhibitory areas arranged side by side

Feature detectors in Striate cortex (aka Simple Cortical Cells) -

1. Simple cells - nonmoving stimulus

2. Complex cells - moving stimulus, up & down across the retina

3. End-stopped cells - moving lines with length or corners/angles

Selective adaptation

Neuron firing decreases when stimulus immediately presented again (short period of time)

Contrast threshold

The light intensity difference where bars can just barely be seen

Selective Rearing

Exposure to certain feature for a long period of time increases neuron firing (e.g. kittens reared in vertical lines box)

Neural plasticity/Experience-dependent plasticity

Neurons can be shaped to respond in a certain way

Spatial organization

How environment stimulus is processed in specific locations of the brain

Retinotopic map

Map of electrical signals going to certain locations in cortex

Cortical magnification

Fovea (i.e large area in striate cortex)

Fovea makes up .01% of retina

Signals account for 8%-10% of retinotopic map on cortex

Columns

Group of neurons firing in specific area of striate cortex

Types of Columns

1. Location - receptive fields in retina are in same location of the striate cortex

2. Orientation - stimulus is positioned in particular direction

3. Hyper - location column with all orientations of a stimulus

Cortical property

Image of stimulus doesn't need to look same way in visual cortex

Neurons in cortex only need electrical info to represent stimulus

Tiling

Location columns working together to cover entire receptive fields

Streams

Pathways leading to brain areas:

What, Where, How

Ablation

Destruction of tissue in nervous system

Object discrimination problem

Ablation related:

Pick the correct shape, temporal lobe, ventral (what) pathway

• (Identifying objects)

Landmark discrimination problem

Ablation related:

Pick food well closer to cylinder, parietal lobe, dorsal (where, how) pathway

• (Location of objects)

Neuropsychology

Study of brain damage affecting behavior

Double association

Patient A: Damage to X area but not Y area

Patient B: Damage to Y area but not X area

Patient D.F.

Had damage to ventral (temporal, what) stream from carbon monoxide poisoning

• Unable to match orientation of her card to the oriented slot

• Holding card & placing it up to oriented slot

• Identified orientation

  • dorsal (parietal, how, action) stream was intact

Size illusion experiment

Shows how people without brain damage can show differences in what/how pathways

• Detecting line differences

Length estimation task

• W/ ventral (what, temporal) pathway

• Falsely assume line #1 is smaller than #2

Grasping task

• W/ dorsal (how, parietal) pathway, perception is accurate

• Fingers detect line #1 longer than #2

Inferotemporal (IT) Cortex

Detects patterns of objects

Hippocampus

Forming & storing memories

Medial temporal lobe (MTL)

Perceiving objects, concepts, and remembering them

Machines & Perception

Machines can’t detect unclear/hidden images unlike humans

Inverse projection problem

Retina able to determine representation of object even if it doesn't look like object in retina (e.g. Textbook at angle)

Viewpoint invariance

Ability to recognize an object from diff. viewpoints (e.g. object is object regardless of position)

Perceptual Organization

How we process elements of an environment in our visual system

Elements of Perceptual Organization

1. Grouping - objects belonging together

2. Segregation - objects separate from each other

Structuralism

1. Build up simple sensory parts (sensation) first

2. Awareness (perception) will occur

Past experiences influence perception

Gestalt Principle

1. "Whole is diff than sum of its parts"

2. Doesn't need building up

Past experience plays minor role

Apparent movement

Illusion of movement when nothing is moving

Illusory contour

Appearance of shape without actual physical edges

Gestalt Organizing Principles

Grouped Things

1. Good continuation - connected points result in straight or smooth curves

2. Pragnanz - "good figure," pattern interpreted simplest way possible

3. Similarity - alike things

4. Proximity - things near each other

5. Common fate - things moving in same direction

6. Common region - elements in same region

   1. Can overpower proximity

7. Uniform connectedness - connected region are perceived as single unit

   1. Can overpower proximity

Perceptual Segregation

Element can be separated from another element

Figure Ground Segregation

Figure: part that stands out

Ground: background of figure

Reversible figure-ground: alternating what you see as figure & ground

Properties of Figure & Ground

1. Figure - stands out as object (memorable) / has shape

   1. Front of ground

2. Ground - Gives a specific shape behind figure

3. Border ownership - contour (border) separating figure & ground

Vecera Experiment

Result:

• To detect where people perceive figure & ground

• Up-down display: down = figure, above = ground

• Left-right display: no preference of figure or ground

Why? More everyday awareness, down area typical scenes like land, and above area typical scenes like background

Peterson & Salvagio Experiment

Result:

• Left-right display, convex (bulging) borders considered figure & not ground

• If non-convex (bulging) side has cue, can be considered figure side due to contextual cues & segregation

Gestalt psychologists believe…

…perceptual organization can override past experience to recognize objects

Gibson & Peterson Experiment

Result:

• Meaningfulness can play important role in recognizing objects

• Familiarity allows people to recognize patterns of an object

Recognition by Components Theory

Biederman: “objects made up of geons” (3D shapes like cylinders, cubes, solids)

Supports viewpoint invariance

But: Not all geons are shaped the same way for objects (e.g. cloud)

Scene and its Components

View of environment

1. Background elements

   1. Acted within (environment)

2. Objects organized in meaningful ways

   1. Acted upon (involves action to objects)

Gist of a scene

Rapid awareness of environment

Perceived at ¼ second/250 ms

Visual masking

Covering info from being seen after stimulus is shown (Prevents persistence of vision)

Persistence of Vision

Image doesn't go away quickly when taken away

Persists another 250ms

Global Image Features (GIF)

1. Degree of Naturalness

   1. Natural scenes - textured zones, wavy contours

   2. Man-made scenes - straight lines

2. Degree of Openness - spacious, fewer objects

3. Degree of Roughness - smoothness

4. Degree of Expansion - convergence of parallel lines

5. Color - colors

Regularities in Environment

1. Physical - regularly occurring physical properties

   1. Oblique effect - horizontal & vertical lines easier to perceive than slanted

   2. Light-from-above assumption - light in natural environment comes from above

2. Semantic - knowledge of regular things in context to a scene

   1. Scene schema - expected things in a regular scene (e.g., in a classroom)

Palmer's Experiment

Result:

• People view a scene & then presented certain objects briefly, items that fit scene schema identified more accurately than items that don't

Helmholtz's Theory of Unconsciousness Inference

Unawareness to interpret stimulus in more than 1 way

Likelihood principle

Objects perceived on what is most likely to have caused visual input (e.g. red & blue rectangles)

Attention

Active process of focusing

Overt attention

Direct focus on an object

Covert attention

Focus something without directly seeing it (e.g. listening to other conversation while taking notes)

Posner Experiment

Result:

• Press button when square is seen

• Faster response to correct precueing (valid trial)

• Slower response to incorrect precueing (invalid trial)

• Processing info more effective when attention is directed

Spatial attention

Focus on specific location

Precueing

Arrows presented before stimulus

Binding & Binding Problem

Features combine to perceive complete object (e.g., color, form, location)

Binding occurs in diff areas of brain

Treisman & Schmidt Experiment

Result:

• Divided attention task, identify #'s on sides/shapes in middle

• Likely to mismatch features of objects after 1/5 of sec, 200ms

Feature Integration Theory (FIT) stages

1. Preattentive stage - features of objects are separated, "free floating" features before perception

   1. Illusory conjunctions - features get "mismatched"

2. Focused attention stage - features are combined into coherent perception

   1. Focusing on objects rids illusory conjunctions

Visual scanning

Looking from place to place (through fovea)

Fixation

Eyes briefly pause to focus on an area

Saccadic eye movements

FAST jerky movement in eyes to focus on one fixation to another

Occurs 3x per sec

Stimulus salience

Stand out/Noticeable

Attentional capture

Involuntary shift of attention due to stimulus salience (e.g. loud bang)

Saliency map

What we notice in our attention based on fixations

Maps out what is fitting for a scene

Influenced by top-down processing

• Fixations influenced by scene schemas; people look at things longer when they're out of place

Task demands

Shift attention based on active task in front of you

"Just in time" strategy

Eyes move ahead before info is needed

Egly Experiment

Result:

• Identify target somewhere on 2 rectangles

• Cues given where target may be

• Faster response to correct cueing, & for incorrect cueing when target is still on same rectangle

• Slower response for incorrect cueing when target is on diff rectangle

Same-object advantage

Better attention when target is already within attention

Carrasco Experiment

Result:

• Identify which grating had higher contrast

• Fixate on dot, another dot shows quickly on one side

• Grating stimuli appears on both sides of fixation dot, report on which has higher contrast

• Different contrast - flashing dot no effect on attention

• Similar contrast - observer reported grating stimulus with flashing dot precue as higher contrast

• Attention can influence perception of appearance

O'Craven Experiment

Result:

• 2 images (house, face) superimposed on each other that switch back & forth

• Have to pay attention to either one

Parahippocampal Place Area

Area of brain firing during pictures of locations

Fusiform Face Area

Neurons fire when focused on faces

Middle Temporal/Medial Superior Temporal Cortex

Brain area where neurons fire upon any environmental movement

Inattentional blindness

Stimulus not perceived even when directly looking at it

Change blindness

Difficulty detecting change in scene