Percepția și designul de experimente

Percepția și designul de experimente

• Percepția și designul de experimente

• Fundamente ale Psihofizicii

Fracțiile Weber sunt adimensionale

• Fracțiile Weber sunt adimensionale

• Este posibil să se compare diferite modalități senzoriale

• Exemplu: luminozitate si intensitatea acustică

Sensory Threshold

• Sensory Threshold

• Herbart (1824) critical boundary, above which neural activity signals the presence of a sensory event –ABSOLUTE

Threshold is a statistical concept, affected by:

• Threshold is a statistical concept, affected by:

• Chance variation in the nervous system
• Random signal noise
• Intensity of signal
• Observer’s criterion

One way of measuring tactile sensitivity is to determine the smallest amplitude of vibration of the skin that can be detected by an observer

• One way of measuring tactile sensitivity is to determine the smallest amplitude of vibration of the skin that can be detected by an observer

• Verrilo’s experiment (1963): a stimulator attached to a vibrator was placed in contact with the base of the thumb

• The size of the stimulator was varied over a range of 0.005 cm2 to 5.1 cm2

When the stimulator was larger then 0.02 cm2, vibrotactile sensitivity was greatest in the frequency region around 250 Hz

• When the stimulator was larger then 0.02 cm2, vibrotactile sensitivity was greatest in the frequency region around 250 Hz

• Increasing the size of the stimulator, the threshold proportionally decreases

• For 0.02 cm2 stimulators or smaller, no spatial summation was observed

From these findings Verrillo concluded that the skin contains at least two receptors systems.

• From these findings Verrillo concluded that the skin contains at least two receptors systems.

• One system summates energy over space and accounts for the U-shaped frequency function obtained when all but the smallest stimulators are used (Pacinian corpuscle)
• The other system accounts for the flat frequency (no spatial summation) for very small contactors

In further experiments stimuli with a much wider frequency range were presented

• In further experiments stimuli with a much wider frequency range were presented

• The results provided the basis for a four channel model of mechanoreceptors (1988)

• P channel (Pacinian) high frequency
• NPI (Meissner) 2-40 Hz
• NPIII (Merkel) 0.4-2 Hz
• NPII (Ruffini) only if Pacinian are deficient

P channel (Pacinian) H.F.

• P channel (Pacinian) H.F.
• NPI (Meissner) 2-40 Hz
• NPIII (Merkel) 0.4-2 Hz
• NPII (Ruffini)