Psychophysics (PP)

Question 1

What is psychophysics (PP)?

Answer 1

-Quantitative discipline mapping psychology upon physics
-Relates perceptual responses of an organism e.g. human or animal to visual, auditory, tactile or chemical stimuli (categorised as physics)
-PP study overall performance of overall visual system by examining visual input/output relationship

Question 2

What is outer psychophysics?

Answer 2

Builds with relationship between stimulus and perception – PP
PP in more classical and narrow sense

Question 3

What is inner psychophysics?

Answer 3

• Builds with relationship between neural events and perceptions evoked by physics
• Indirectly find shared brain region or activity when they are going through the same perceptual experience
  o e.g. fMRI imaging – used to correlate perception to brain activity without having to open the skull and place electrodes into head
  o Measure brain activity when px is shown colour patch to see what relationship there is to a specific colour
   If can find a common brain region/activity with respect to a specific colour across people, then can be more confident in relationship between brain region and perceptual experience
• Direct Brain Activity Recording:
  o Multielectrode array implanted into px’s head by surgery
  o When px looks at screen to do task, brain activity is then directly recorded from electrodes

Question 4

Describe combining both inner & outer psychophysics?

Answer 4

• Historically, long tradition of physiology to identify internal structures by breaking system open and dissecting it into smaller pieces
• This is not best way to understand system that way
• Was recognised that behaviours displayed at the systems level, may not be apparent at the level of individual components that make up the system
• May be too complicated to describe the behaviour displayed at the systems levels by considering the induvial components in isolation

Question 5

Describe outer psychophysics as a Systems Science?

Answer 5

• People are more interested in what a system does rather than what it is made of
• For such a complex system like the visual system, simple summation of individual parts is not adequate to explain function of visual system as whole
• Major goal of systems analysis is to come up with mathematical model of a system to predict an output when it is given a specific input
• From this line of thinking, psychophysical approaches may trick visual system as a “Black Box”
  o In a typical Psychophysical experiment – a precisely controlled input (e.g. visual input (luminance, contrast, or colour) is presented to system and output is measured from the subjects response (percent correct, rating)
  o From this input and output relationship, the functional characteristics of the system can be determined without much consideration of what’s actually inside visual system to process the input
  o With appropriate and careful appraisal of input and output, the performance of human visual system can be understood with relative straight forward mathematics and functionally plausible components

Question 6

Describe systems properties of vision?

Answer 6

• Shown picture of fine gratings & looking to see if can resolve another image behind them
• If resolved the image, info physically present in the stimuli must have retained or relayed through a series of anatomical or physiological causal chain of events leading to a conscious perceptual experience
• If did not resolve image, info must have been lost somewhere inside the system
  In absence of knowledge about inner working of the “Black Box”, system properties of vision puts fundamental constraints on models of how it works