PART B: Two-Point Discrimination Threshold

What is the two-point discrimination threshold?

defined as the minimum distance between two stimuli that can be detected as separate points

What is the basis of it?

the density of tactile mechanoreceptors and the size of their receptive fields in the skin, which determines the minimum distance required to perceive two distinct, simultaneous stimuli rather than one

What did we use to measure it?

drawing compass as the two points

metric ruler to measure the distance between them in millimeters

What is the receptive field?

the number of receptors that terminate on one sensory neuron; anything within the same receptive field is sent as one

What determines the ability to distinguish between the two points?

To perceive the two distinct points, each point must touch a different receptive field to be transmitted by two different sensory neurons to the brain

What causes the perception on one point?

if both points fall within the same receptive field (stimulating the same sensory neuron), the brain will perceive them as a single point of touch

What influences the ability to distinguish between the two points?

1) Receptor density: the greater the number of receptors in given area, the better at discriminating between stimuli

2) Receptive field size: inversely proportional to the density; the greater the receptor density, the smaller the receptor field, which allows for finer discrimination

3) Physical characteristics: size and shape of receptor

Larger the two point discrimination threshold?

large the receptive field, making the area less sensitive

Smaller the two point discrimination threshold?

small the receptor field, making the area more sensitive

How did the results compare between the various body parts (fingertip, palm, back of hand, and back of neck)

Threshold: fingertip<palm<back of hand< back of neck

• larger the threshold the larger the receptive field (less neurons, less sensitive)

Receptor density: finger> palm> back of hand> back of neck

• higher density, smaller the size = smaller threshold (more neurons, more sensitive)

Where is the sensory information sensed? Why do some have smaller/larger thresholds?

sensory information from the skin is sent by the sensory neurons → interneurons of spinal cord → thalamus → to the somatosensory cortex

Sensory cortex has more/less space for each body part; more reserved to fingers/hands because we do a low with them and want to feel that

less space for the trunk/limbs because we don’t do much with them, do not require high sensitivity