Download Psychophysics ppt. - Ms. Engel @ South

Sensation (psychophysics)
Transduction, Thresholds, and
Coding
Do Now
• Answer the
following question:
– If a tree falls in a
forest and no one is
around to hear it,
does it make a
sound?
Sensation: the process by which
physical energy is transduced into neural
responses
Psychophysics: the study of the
relationship between physical stimuli and
the mental or physical experiences the
stimuli evoke
Key ideas: transduction and coding
Three steps of sensory processing:
Physical stimulusPhysiological responseSensory
or psychological experience
• Physical stimulus: light energy, sound energy,
pressure, chemical (taste), etc
• Physiological response: receptor potential in
the sensory receptor which causes a change
in the release of NT which modifies the firing
rate in neurons with which these cells form
synapses and so on until the information
reaches the brain
• Sensory experience: see color, taste bitter,
hear low tone
Touch as Example
• Receptor field
– Activate/deactivate
• Excited in central area
• Inhibited in surrounding area
•
•
•
•
Sensory neuron
Brainstem
Contralateral thalamus
Primary sensory cortex (raw data)
– Topographical parts relative to body
– Complexity and integration on ascent
• Posterior parietal cortex
– Integration with other senses
• EX: cats only respond to site and sound of birds
Thresholds
• What is a sensation?
– Just the stimulus present?
– Just the mind reaction?
– Behavioral definition: absolute threshold where stimuli is identified 50%
of the time
• Attention key
• Signal detection theory
– Response bias
» Need for multiple trials
• Sensory adaptation
• Just noticeable difference (JND)
• 1/30 for weight, 1/100 for length
• Weber’s law
• Amounted added causing JND is dependent on the amount of a stimulus
already present
• the jnd for a stimulus magnitude is a constant proportion of the
magnitude of the original stimulus
Sensory Transduction
•Transformation of one form of energy
into another
•Sensory events are transduced or
transferred into changes in the cell’s
membrane potential
•Example: Light energy is transformed
by an electrical chemical interaction
in the sensory receptor into a
receptor potential
Quantitative Dimension
– Amount or intensity of energy
present
• Dull or bright light, light or
strong pressure, loud or soft
tone, strong or weak bitter
taste
– Rate of firing and number of
neurons
– Different neurons for different
intensities
• Neuron 1: low threshold for
small distinctions
• Neuron 2: medium threshold
• Neuron 3: accurate for strong
stimulus
Qualitative dimension
– Precise kind of energy present
• Red or yellow light, sweet or
bitter taste, high or low pitched
tone
– Different receptor neurons are
differentially sensitive to different
kinds of energy
• Quantitative: magnitude
• Qualitative: relative firing
Coding
Processing
•Sense-specific
Processing center,
sensors, and
pathways
•Convergence
•As information
proceeds up the
brain, it is
integrated and
more complex
Revisit Do Now
• Did the tree make a sound?
– What might psychologists say?