Sensation & Perception

• Ch. 1-3: Review

© Takashi Yamauchi (Dept. of Psychology, Texas A&M University)

Rat-man demonstration

What does this tell?

Why do we see two different things (a rat or a man)?

• An interaction between

– attention and perception

– cognition and perception

• Tell me what you see.

• Tired

• Old

• Sick

• Dark

• Slow

• Heavy

• Hospital

• ugly

• death

• Beautiful

• Young

• Fresh

• Fast

• Energy

• Juicy

• Clean

• cheerful

• Vigorous

Ch 1 10

How come?–Different types of physical information (air vibration, light energy) are translated into a common language in the brain– neural information

Environmental Stimuli (e.g., light energy)

Transduction

Neural Processing

Perception

• What does this circle tell you?

• How are the circle and the rat-man demonstration related?

• Levels of analysis

– Psychological level– Physiological level

– Single cell recording– EEG/ERP– PET Scan / fMRI– What are they?

Single cell recording

PET & fMRI

fMRI Setup

• Detection– Absolute threshold

– Difference threshold

• Can you define them?

• DL (difference threshold)

• Weber’s law

The impact of standard stimuli

• DL (difference threshold) gets larger as the standard stimulus gets larger.

• Weber’s lawDL/S=K

• DL: difference threshold• S: standard stimulus• K: constant

Weber’s law

Question:

• With a standard stimulus 1 kg, John’s difference threshold was 0.25kg. With a standard stimulus 10kg, what would be John’s difference threshold?

Question:

• With a standard stimulus 1 kg, John’s difference threshold was 0.25kg. With a standard stimulus 10kg, what would be John’s difference threshold?

DL/S=K

•DL: ?

•S: 10

•K:

DL/S=K

•DL: 0.25

•S: 1

•K: 0.25

Magnitude estimation

• What is it?

Magnitude estimation

Magnitude estimationStandard: == 10

Target: == ?

Standard: == 100

Target: == ?

Steven’s power law

• P = K S^nP: perceived magnitude

K: constant

S: stimulus intensity

n: a power

Neurons

Dendrites

Cell body

Axon

• Neuron• Neurotransmitter• Synapse• Action potential• Dendrites• Axon• Cell body• Excitatory and inhibitory connections

Rods and cones

• Morphology

• Their roles

• Distribution on the retina

• Their connections

Photo receptors: Rods and cones

The distribution of cones and rods on the retina

• Cones are concentrated mainly on the fovea.

• There are no rods on the fovea.

• We move eyes to capture images on the fovea.

• Convergence:– The ratio of connections with two groups of

neurons.– Rods vs. Ganglion cells

• 120:1

– Cones vs. Ganglion cells• 6:1

Why does this matter?

Time0 t

The frequency of action potential

Time0 t

The number of action potential emitted by a neuron is correlated with the intensity of the stimulus.

Time0 t

• How do you detect there are two separate dots (lights)?

Questions: What happens to B?

Questions: What happens to B?

Excitatory Inhibitory

Questions: What happens to B?

Receptive field• The receptive field of a neuron in the

visual system is the area on the retina that influences the firing rate (action potential) of the neuron.

• Measuring the receptive field of a ganglion cell

Measuring a receptive field of a ganglion cell

Change the size of the stimulus and see the way a ganglion cell respond

Cones Ganglion cell

B

12 3 4 5 6 7

=sum(B)

=sum(B)

Physical stimuli Your perception

Lateral inhibition

Lateral inhibition

(a)= -h’ + h -h’

(b)= -h’ + h -l’

(c)= -h’ + l -l’

(d)= -l’ + l -l’

h > l

h’ > l’, -h’<-l’

H L

H H H L L L

h h h l l l

h’ h’ h’ h’ h’ l’ l’ l’ l’ l’h’ l’

(A) (B) (C) (D)

(a) (b) (c) (d)

(a)<(b), (c) <(d)

Lateral inhibition

(a)= -h’ + h -h’

(b)= -h’ + h -l’

(c)= -h’ + l -l’

(d)= -l’ + l -l’

h > l

h’ > l’, -h’<-l’

H L

H H H L L L

h h h l l l

h’ h’ h’ h’ h’ l’ l’ l’ l’ l’h’ l’

(A) (B) (C) (D)

(a) (b) (c) (d)

(a)<(b), (c) <(d)