Lecture Summary
-Form Perception (Gestalt)

-Depth and distance cues

-Perceptual Constancies

-Pain and Skin senses

-Nature / Nurture inborn vs. culture

-Puzzles of perception (blindsight & ESP)

Form Perception

Gestalt -Pattern of form usually figure-ground relations. E.g., Music or Orchestra or band - Whole is greater than the sum of its parts.

Gestalt Principles of perceptual organisation:
1.) Proximity - closeness

2) Closure - making a solid form

3) Similarity - same appearance

4) Continuity or Pragnanz - smooth flow of form

 Depth and Distance Cues

Convergence (of the eyes) the moving of the eyes

- muscular feedback

Retinal Disparity - different images from eyes

Interposition - standing in front of another
Linear Perspective-convergence of parallel lines
Relative Size Depth Illusion - larger is perceived as closer
Texture Gradient - (d) coarse is near, smooth is far

Motion Parallax - close move fast and opposite to us, far move slowly in same general direction
Perceptual Constancies: Our perceptual systems keep these constant in perception.  See Beau Lotto's talk from Ted talks

1) Shape, 2) location, 3) Brightness, 4) Colour, b 5) Size.

Perceptual Illusions: an erroneous or misleading perception of reality that vary systematically. e.g., Phi Phenomenon, Muller-Lyer (alt.) , Ponzo, impossible figures, .... Everydayexamples Twirlingdancer

Figure and Ground relationship play an important role.  When we perceive objects they usually have some kind of context against which they are perceived.  Reversible figure have changing figure-ground relationships where the figure becomes the background and the background becomes the figure.  
E.g.  The faces vase, the old woman/young woman, . ..

Senses of the Skin: Touch (pressure) warmth, cold, pain. Once thought to be different cells for each, now thought to have different codes.


Gate Control Theory of Pain Signals passing through the spinal chord "gate" to brain lead to experience of pain. Some neurons open and some close the (inhibitory) gate.

Three Components
to the Gate
  Two fibres and one interneuron
Slow- small  Inhibitory Fast  large fibre pressure 
dull or chronic pain  Inter-
"emergency" signals
-fast "closing' fibres can be stimulated by massage to stop the fast searing pain by activating the inhibitory inter-neuron.

-also have descending cortical nerves to close gate

-slow (small) fibers inhibit the inhibitory inter-neuron and activate the projection (pain) neuron, opening the gate and giving PAIN

Phantom Pain - aching, burning or sharp pain in a limb or organ that had been amputated. Why?  See video from TED Talk of VS Ramachandran start @3:00 (prt2)

Two possibilities:
1) Impulses that had previously closed the gate are reduced or lost

2) Once pain producing activity begins in the brain it continues without sensory input (being stimulated by neighbouring brain areas-i.e., face-hand)

3) Other brain parts are "calling" the missing limb.

Anomalies: People born with missing limbs have never had normal sensory experiences why do they experience phantom fingers or toes?

Nature vs Nurture and 
the Origin of Perception

Cat studies - translucent goggles (or darkness, lines) visual impairment e.g., (|||||||)

Normal experience insures that the development of perceptual abilities will lead to survival.

Critical periods for development (or atrophy) Hebb's dogs - could not feel pain, Jeannie - language.

Visual Cliff
- 2 months slowed heart rate when over deep side

- 6 months old don't cross over to the deep side

 Cultural and Psychological Influences on perception

Needs / Affordances - perceive objects more readily, e.g., poor children recall money bigger

Beliefs - think true will be seen x-files -- ufo

Emotions - fear of snakes in darkness shows that - a rope and coat become snake and ghost

Expectations - perceptual set a habitual way of perceiving, based upon expectations e.g., typos in an essay 'univarsity' goes un-noticed. As in Beau Lotto video -

"Ca _y u _re d _t is ?" and "Y ou a e not r adi g th s."

Cultural Studies:
Susceptibility to illusions is affected by past experience.

E.g., Muller-Lyer & carpentry

Puzzles of Perception
Conscious and non-conscious perception
Blindsight in people with damaged visual cortex don't 'see' but respond better than chance  You Tube-Ramachandran

Doctors speaking during operations

Below threshold Subliminal perception
- may help with perception of related word but not buying habits. It is not subliminal persuasion however the mere exposure effect may be present. (listened to audio).

Telepathy - is direct communication from one mind to another.

Clairvoyance - is the perception of an event or fact without normal sensory input

Precognition- is the perception of an event that has not yet happened

Out of the body experiences - perception of one's own body from the 'outside'

See activities for tests of this.

Evidence or Coincidence?
Parapsychology is the study of purported psychic phenomena such as ESP and mental telepathy.  Whether or not it exists is usually determined by the probability of such events occurring by chance.  If the results are well beyond what are expected by chance it appears that something is going on whether or not it really is ESP.

Ganzfeld procedure
-sender and receiver each in sound proof rooms get 'random' picture and pick image out of four.

Bem & Horton found 33% hit rate (chance was 25%) !

Transgressions of "Magic"
Magician James Randi has worked extensively to debunk Uri Geller as Easy 'tricks', cold reading, slight of hand