The Perceptual Process (SLRNPRA)

1. Stimulus in the environment

   1. Distal and Proximal Stimuli
      (Steps 1 and 2)

      1. Distal Stimulus

         1. Environmental stimulus are all objects
            in the environment are available to
            the observer.

         2. Observer selectively attends to
            objects.

         3. Stimulus impinges on receptors
            resulting in internal representation.

2. Light is reflected and focused

   1. proximal stimulus

      1. focuses on the energy falling on a receptor surface

3. Receptor processes

   1. Sensory receptors are
      cells specialized to
      respond to environmental
      energy

   2. Visual pigment is what
      reacts to light

   3. Transduction occurs,
      which changes
      environmental energy to
      nerve impulses

4. Neural processing

   1. Neural processing: changes
      that occur as signals are
      transmitted through the maze
      of neurons

   2. Primary receiving area

      1. Occipital lobe

      2. Temporal lobe

      3. Parietal lobe

5. Perception

   1. organization, identification, and interpretation of sensory information

6. Recognition

   1. the act of recognizing or the condition of being recognized.

7. Action

   1. Experience and Action

      1. Electrical signals are transformed into conscious experience.

      2. Person perceives object (such as a tree)

      3. Person recognizes it as a tree (places object in category).

Knowledge: any information the perceiver brings to a situation

Bottom-up processing

Processing based on incoming stimuli from the environment

Also called data-based processing

Top-down processing

Processing based on the perceiver’s previous knowledge (cognitive factors)

Also called knowledge-based processing

**Perception is determined by an interaction between:
**Top-down processing, which brings the observer’s knowledge into play
bottom-up processing, which starts with the image on the receptors.

**Studying the Perceptual Process
**observing perceptual processes at different stages in the system:
PSYCHOPHYSICAL LEVEL OF ANALYSIS
Relationship A: the stimulus-perception relationship

ex: A violin and an oboe play the same pitch, 440 hz. Do they sound the same?

PHYSIOLOGICAL APPROACH
Relationship B: the stimulus-physiology relationship

ex: When different pitches are played, different receptors along the Organ of Corti fire
Relationship C: the physiology-perception relationship

ex: When different receptors fire, you report if a note sounds “high” or “low”

The key to understanding all of this is to:

1. know what question you want to ask

2. recognize what is being measured

PSYCHOPHYSICAL Ways to Measure Perception
Gustav Fechner(mid 1800’s physicist)
Called it “psychophysics” for short
Published Elements of Psychophysics (1860)

Qualitative Methods
Describing
Recognizing
Quantitative Methods
Detecting
Perceiving Magnitude
Searching

Qualitative Methods of Psychophysical Measurement
Description
Indicating characteristics of a stimulus
First step in studying perception
Called phenomenological method
Recognition
Placing a stimulus in a category by identifying it
Categorization of stimuli
Used to test patients with brain damage

Quantitative Methods of Classical Psychophysics
Detection
Absolute threshold- smallest amount of energy needed to detect a stimulus
Method of Limits(“Can you hear me now?”)
Method of Adjustment
Method of Constant Stimuli

Something to Consider: Is There An Absolute Threshold?
There are differences in response criteria among
participants
Liberal responder- responds yes if there is the
slightest possibility of experiencing the stimulus
Conservative responder- responds yes only if he
or she is sure that a stimulus was present
Each person has a different response criterion but
the sensitivity level for both of them may be the
same
Signal detection theoryis used to take individual’s
response criteria into account.

Difference Threshold (DL)
The minimal detectable difference between two stimuli
Measured using the same methods
Also measured using Weber’s (a physiologist) methods
Weber was Fechner’s teacher

Difference Threshold (DL)
Subjects are presented a standard stimuli and then presented a
comparison stimuli and asked to judge the difference
When the difference b/n the two is small, the difference is difficult
to detect
As the magnitude of the stimulus increases, so does the size of the
DL

Just Noticeable Difference (JND)
Psychophysical Methods
These psychophysical methods have other historical value
Represented the first time in the history of scientific psychology that mental activity could be measured quantitatively

Quantitative Methods - Modern Psychophysics
Perceiving Magnitude
Stimuli are above threshold.
Observer is given a standard stimulus and a value for its intensity.
Observer compares the standard stimulus to test stimuli by assigning numbers relative to the standard.

Quantitative Methods - Modern Psychophysics
Magnitude estimation (cont.)
Response compression
As intensity increases, the perceived magnitude increases more slowly than the intensity. (ex: brightness)
Response expansion
As intensity increases, the perceived magnitude increases more quickly than the intensity. (ex: electric shock)

Other Measurement Methods
Searching for stimuli
Visual search- observers look for one stimulus in a set of many stimuli
Reaction time (RT) - time from presentation of stimulus to observer’s response is measured

Why study this?
Because the physical stimuli and what we perceive don’t always
match
That’s the conclusion that Fechner reached on October 22, 1850