Introduction / The Perceptual Process

Perception seems effortless and automatic
Steps in the perceptual process: (e.g., vision)

1. light bounces off object...
2. into your eye to from image on retina which...
3. generates electrical impulses in receptors and creates...
4. nerve impulses which travel along nerve fibers to...
5. reach the brain where they are...
6. 'processed', creating the...
7. perception

Perception (and all we know of Reality) happens in your head - Interaction of physical stimuli with sense organs
Energy from the environment in the form of :
sound (vibrations of air molecules), light (radiation), mechanical (pressure), chemical (molecules of object for taste and smell)

- Stimulus can have four main properties for detection:

1. MODALITY (What?)
   Vision: electromagnetic energy perceived as light
   Somatosensation: mechanical pressure on skin
   Audition: pressure waves in air
   Smell and taste: molecules of matter
   
2. INTENSITY (How Much?) - How weak or strong is the stimulus?
3. LOCATION (Where?) - Where is the stimulus coming from in relation to the organism?
4. DURATION (When or How long?) - What is the onset/offset of the stimulus?
   When did it start, How long did it last, is it still present?)

The brain is a filter for the immense energies coming at us (electromagnetic spectrum, sounds, magnetic fields, etc.)
Top-Down -vs.- Bottom-Up Influences on How we perceive the environment
Top-down - how previous experience, expectation, and other cognitive effects influence perception
Bottom-up - how the physical properties of the stimulus limit and control our ultimate perceptions

THE PERCEPTUAL PROCESS:
Distal Stim, Proximal Stim, Transduction, Processing, Perception, Recognition, Action

( reality.....physical energy..neural energy...calculation.........percept...........memory........approach / avoid )

Perception is the means of survival
Why Study Perception?

1. Scientific Curiosity
2. Diseases/disorders/malfunctions - Helping those with perceptual difficulties
3. Technology (robots, etc.)
   - Electric Eyes or Sensors (based on motion-detection in the frog eye)
   - Mirror Telescope (based on contrast-sensitive horseshoe crab eye)
   - Synchronous Lenses: for microsurgery, optical scanning, severe vision problems (based on double lens of a crustacean)
   - Computer Applications - robotic assembly, voice recognition, remote guidance for space probes, Virtual Reality
4. Safety Issues: How pilots see in bad weather, designing equipment with good visual displays, etc.
5. Two fundamental approaches to the study of perception
   

Two Fundamental Approaches to Studying Perception

* Psychophysical Approach - the Stimulus side: How do we use information from the environment to create perceptions?
* Physiological Approach - the Organism side: How are properties of stimuli in the environment represented by activity in the nervous system?

PSYCHOPHYSICS
Finding quantitative relationships between physical stimuli and our perceptions
Gustav Fechner (1860) Elements of Psychophysics
Absolute Threshold: smallest amount of stimulus energy needed for an observer to detect that stimulus
Fechner's 3 Methods of Psychophysics
Error and Threshold Estimation
.................1)...Limits - increase stimulus intensity until subject says they detect;
......................decrease stimulus intensity until subject says they do not detect
......................where these two measures meet = subject's threshold

fastest------>2)...Adjustment-subject or experimenter gradually changes intensity
least acc.         best if subject does it, turns it up (or down) until barely detectable
slowest----->3)...Constant Stimuli - similar to limits, but diff. intensities presented
most acc.         in random order; detection on 1/2 of trials = threshold
Why do you average the "yes" and "no" responses across trials? Errors of Preservation

Ernst Weber
Just Noticeable Difference (JND): smallest difference between 2 stimuli a person can detect
Weber's Law: as the magnitude of the stimulus increases, so does the size of the JND
JND between 100 and 105 grams (5g); 200 and 210grams (10g)
Weber's Law: JND/S=K (K is constant called the Weber fraction; S is the value of the standard stimulus)...K=5/100=.05, K=10/200=.05
Weber's law seems to hold for many of the senses

S.S.Stevens - measuring above threshold
Magnitude Estimation
Standard stimulus gets rating value (brightness = 5), subject then assigns subjective value to new stimulus ("it's about twice as bright"=10)
Straight line= linear response, slope near 1.0; apparent line length
Curves that bend down= response compression, doubling light intensity causes less than a doubling of subjective brightness
Curves that bend up= response expansion, doubling strength of shock causes more than a doubling of the sensation
These are described with logarithmic plots or power functions
Steven's Power Law: P = KSn
..............................perceived magnitude = constant K * S (stim intensity) to the n power (from experiments for that stimulus)

<<< FIGURE: Graph of Magnitude Estimation Relationships >>>

PHYSIOLOGY

Doctrine of Specific Nerve Energies: our perceptions depend on nerve energies reaching the brain and that the specific stimuli we experience depends on which nerves are stimulated

Otto Loewi (1873-1961) Showed that frog heart could be inhibited (or excited) by submerging it in a solution which had prev. bathed another heart inhibited by vagus nerve stimulation (or excited by sympathetic nerve stimulation)

BASIC NEUROANATOMY
Dendrite, Soma, Axon

<<< FIGURE: Basic Structure of a Neuron >>>

Recording Electrical Signals in Neurons
Concentration gradient - Na+, Cl-, and K+
Action Potential - Threshold, Firing, Refractory Period

<<< FIGURE: Graph of the Action Potential >>>

<<< FIGURE: Concentration Gradient and Action Potential >>>

Basic Properties of Nerve Impulses
Propagated response: once triggered, impulse travels all the way down the axon
All-or-none law: once triggered, it stays the same regardless of the distance it travels or how intense the stimulus was
Stimulus intensity will not affect strength of impulse but the rate of nerve firing
Spontaneous activity
Chemical and Electrical Events at the Synapse
Most of our knowledge of nervous system developed in the last 100 years

e.g. 'Reticularists' Vs 'Neuronists' around the late 1800's
Camillo Golgi - direct connectivity in a vast network
Santiago Ramon y Cajal - separated by small gap; electro/chemical comm
Both shared Nobel Prize in 1906 for their work

<<< FIGURE: Communication Between Neurons >>>

Pre- and post-synatpic neurons
Neurotransmitters
Synaptic vesicles
Excitation or Inhibition
Network and synaptic summation

<<< FIGURE: Details of the Synapse >>>

The Brain and Perception
How can a neuro-electrical signal = the color blue OR the sound of a guitar?
Localization of Function: specific brain areas seem to serve specific functions
Primary sensory areas in cerebral cortex (and memory, emotion, etc.)
Frontal, Parietal (somatosensory), Temporal (auditory), and Occipital (visual)
Thalamic nuclei
Sensory Coding: the characteristics of nerve impulses and patterns that represent stimuli in the environment