COGLAB RESULTS: MAPPING THE BLIND SPOT

How do we makeup for the blindspot?

1) our other eye

2) we move around

3) our brain puts what we think would be there

Cornea

The transparent “window” into the eyeball

Aqueous humor

The watery fluid in the anterior chamber

Crystalline lens

The lens inside the eye, which allows changing focus

Pupil

The dark circular opening at the center of the iris in the eye, where light enters the eye

Retina

a light-sensitive membrane in the back of the eye that contains rods and cones, which receive 

The Retina

·      Light is received by two receptors

·      Types of photoreceptors on the retina are rods and cones

Rods: Photoreceptors that are specialized for night vision

                  Respond well in low lighting

                  Do not process color (good for night vision)

                  On the propherial of our eye

Cones: Photoreceptors that are specialized for daylight vision

                  Fine visual acuity and color

                  Responds best with lots of light

·      Neural signal reaches ganglion cells from amacrine and bipolar cells

·      Ganglion cells transmit this signal to the brain via their axons that emerge together as the optic nerve

Receptive Fields of Ganglion Cells

·      Receptive fields of ganglion cells look like doughnuts

·      When a light is flashed on these receptive fields, the ganglion cells change their firing rate from a baseline

·      These receptive fields and their properties were found by Hubel and Wiesel (1960) at Harvard University

Lateral Inhibition

·      Excitation of a neuron inhibits the neural activity of neighboring neurons

Receptive Fields in Striate Cortex

Many cortical cells respond especially well to:

Moving lines

Bars

Edges

Gratings

Direction of motion

Feature detectors

neurons that respond best to a specific stimulus

Distributed coding

representation by a pattern of firing across a number of neurons

Specificity coding

representation of a specific stimulus by firing of specifically tuned neurons specialized to just respond to a specific stimulus

Hubel and Wiesel

Found systematic, 

progressive change in preferred orientation

(the orientation of the bars set off different neuron firings)

Bottom-Up Processing

·      Perception may stat with the senses

·      Incoming raw data

·      Energy registering on receptors

Top-down processing

·      Perception may start with the brain

·      Person’s knowledge, experience, expectations

Sensation

absorbing raw energy (e.g. light waves, sound waves) through our sensory organs

Transduction

Attention

concentration of mental energy to process incoming information

·      Some information is more important than other

Perception

selecting, organizing, and interpreting these signals

Sensation and Perception

·      Energy contains information about the world (usually incomplete, full of noise, and distorted)

o   ~~Accessory structure modifies energy

o   Receptor transduces energy into a neural response

o   Relayed to specialized areas of the cortex

o   Perception of the world is created

·      Sensory nerve transmits the coded activity to the central nervous system

·      Thalamus processes and relays the neural response

·      Relayed to specialized areas o the cortex

·      Perception of the world is created

Perception Is..

The process of recognizing, organizing, and interpreting information from sense

Not an exact copy of “the world”

Based on expectation and experiences we’ve had

Approaches to Understand 

Perception

Direct perception theories

–Bottom-up processing 

–Perception comes from stimuli in the 

environment

–Parts are identified and put together, and then 

recognition occurs

Bottom-Up Processing: Behavioral

Recognition-by-components theory (RBC)

·      We perceive objects by perceiving elementary features

·      Geons: three-dimensions volumes

·      Objects are recognized when enough information is available to identify object’s geons

Geons

§  Discriminability: geons can be distinguished from other geons from almost all viewpoints

§  Resistance to visual noise: geons can be perceived in “noisy” conditions

§  Distinct: 36 different geons have been identified

Top-down Processing (Constructive Perspective)

·      Top-down processing involves making inferences based on context, guessing from experience, and basing one perception on another

·      Occurs quickly, automatically

·      EX/ the ebbinghaus size illusion, the same sized dots surrounded by large/small dots

o   context information feeds into your perception

Helmholtz’s Theory of Unconscious Inference

·      Top down theory

·      Some of our perceptions are the result of unconscious assumptions we make about the environment

o   We use our knowledge to inform our perceptions

·      We infer much of what we know about the world

Laws of Perceptual Organization

Pragnanz/law of simplicity, similarity, good continuation, proximity, occlusion, smallness, familiarity

Gestalt laws often provide accurate information about properties of the environment

·      Reflect experience

·      Used unconsciously

·      Occasionally misleading

·      Gestalt laws are heuristics

Gestalt's laws should be called 'heuristics': a rule of thumb

Law of Pragnanz/ Law of Simplicity

·      Every pattern is seen in as simple a way as possible

Law of Similarity

·      Similar things are grouped together

·      Similarity in lightness, shape, color, size, and orientation cause grouping

Law of Good Continuation

·      Connected points result in smoothly curving lines

·      Points are seen as they belong together

·      Lines follow smooth path

Law of Proximity

Things that are near to each other are grouped together

Law of Occlusion

·      When a large object is partially covered by a smaller occluding object, we see the larger one as continuing behind the smaller object

Law of Smallness

Smaller areas tend to be seen as figures against larger backgrounds

Law of Familiarity

·      Things are more likely to form groups if groups appear familiar or meaningful

physical regularities

semantic regularities

Monocular Depth Cues

cues which require only one eye

Patterns of light and shadow

Linear Perspective: the perception that parallels lines converge in the distance

 Relative Size: if two objects are of similar size, the one that looks smaller will be judged to be farther away

 Interposition: objects closer to us may cut off part of our view of more distant objects

·      Height in the horizontal plane

·      Texture

·      Clarity: clear objects are judged to be closer

·      Motion Parallax: if we are moving, nearby objects appear to move faster than faraway ones

Perceiving Size

Perceived size is a function of both bottom-up and top-down processing

·      Bottom-up processing

o   The size of the image on the retina

·      Top-down processing

o   The perceived distance of the object

o   The size of the object relative to other objects in the environment

Perception of Movement

·      Primary Cue for Perceiving motion is the movement of the stimulus across the retina

·      Stroboscopic movement: illusory movement produced when a light is briefly flashed In darkness and the, a few milliseconds later, another light is flashed nearby

·      Principle behind motion pictures

dissociations

situations in which one function is absent while another is present (like in a damaged brain)

·      Damage to different areas of the brain cause very different deficits

o   We can conclude that a specific area is necessary for a specific function

·      Brain Ablation method allows scientists to damage specific areas of otherwise normal brains (usually in monkeys or cats)

o   Controlled damage allows for clear conclusions to be drawn

single dissociation

o   One function is lost, another remains

§  EX/ Monkey A has damage to temporal lobe. This monkey is no longer able to identify objects (what) but can still identify locations (where)

o   Therefore, what and where rely on different mechanisms, although they may not operate totally independent of one another

Double dissociation

o   Requires two individuals with different damage and opposite deficits

o   EX/ Monkey A with temporal lobe damage has intact where but impaired what; Monkey B with parietal lobe damage has intact what but impaired where

o   Therefore, what and where streams must have different mechanisms AND operate independently of one another