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Senses
Sensory modalities in human
Sensory processing
Levels of organization uderlying
sensory processing:
I.
Receptors
II.
Sensory circuits and pathways
III.
Sensory perception
Receptors
stimulus
transduction of the
sensory stimuli
impulse initiation
Receptor potential
Receptor potential in a muscle stretch receptor
(mechanoreceptor). A. These receptors signal
muscle length and the speed at which the muscle is
stretched. The receptor consists of a bundle of
specialized muscle fibers enclosed by a capsule.
The sensory nerve endings respond to stretch of the
muscle fibers. Mechanical deformation of the
membrane opens the stretch-sensitive ion channels.
The influx of Na+ and Ca2+ depolarizes the nerve
ending, producing the receptor potential.
B. Upper records: depolarizing receptor potentials
recorded from the sensory axon (APs have been
blocked with TTX) when the muscle spindle is
stretched to different lengths. Lower records:
amplitude and rate of stretch. The initial
depolarization of the receptor in response to change
in muscle length (dynamic response) is
proportional to both the rate and amplitude of
stretch. When stretch is maintained, the receptor
potential decays to a lower value proportional only
to the amount of stretch (static response).
C. Patch clamp records of a single stretch-sensitive
channel. As the pressure on the membrane is
increased, the channel opens more often and
remains in the open state for longer time intervals.
Stimulus encoding
Receptor potential and impulse frequency
exhibit close correlation.
Stimulus
intensity
Intensity coding in skin touch receptors. Left: in slowly adapting
mechanoreceptors the firing rate is higher at the beginning of skin
contact than during steady pressure. Right: rapidly adapting
mechanoreceptors respond only at the beginning and end of the
stimulus, signaling the rate at which the stimulus is applied or
removed. The receptor is silent when the indentation is maintained
at a fixed amplitude.
Firing rate
Hierarchical information processing
Basic rules:
I.
Divergence
II.
Converrgence
III.
Parallel processing
IV.
Feedback
Connections
Connection patterns between neurons:
a)
Converrgence
b)
Divergence
c)
Serial processing
d)
Parallel processing
e)
Selfeedback
f)
Excitatory positive feedback
g)
Inhibitory positive feedback
h)
Negative feedback
Synaptic triad
Synaptic triad: input elements, relay neurons, intrinsic neurons,
Microcircuits
Examples of synaptic triads in senosory systems. There are input elements (the receptors) and output
neurons (A; ganglion cells, B: mitral cells). There are interneurons for straight-through transmission and
there are interneurons for horizontal interactions. The horizontal connections are organized at two levels.
In both cases there is provision for straight-through transfer of signals to the output neuron and local
processing of signals through the interneurons.
Limulus (skrzypłocz)
Limulus - Atlantic horseshoe crab
The blood of horseshoe crabs contains one type of blood cell,
the amebocytes. These produce visible reaction when exposed
to some bacteria. It is used to detect bacteria and fungi and to
test for several bacterial diseases, e.g., by astronauts in the
International Space Station.
The blood of horseshoe crabs contains the
copper-containing protein hemocyanin, which
is dark blue when oxygenated.
Lateral inhibition
Limulus has been extensively used
in research into the physiology of
vision. The Nobel prize in
Medicine was awarded in 1967 in
part for research performed on the
horseshoe eye.
A.The compound eye of Limulus consists of some 800 receptor units, called
ommatidia. Each ommatidium has 10-15 receptor cells (retinula) arranged in
a circle around eccentric cell, which is the main output cell. Eccentric cells
are connected by dendrodendritic synapses mediating lateral inhibitory
interactions. B. Pattern of activity in population of eccentric cells in response
to light – dark edge stimulus. The enhancement of response on the light side
of the edge and depression on the dark side are due to inhibitory interactions.
Lateral inhibition
A. Surface of the Limulus eye with rectangular stimulus pattern. B. Recordings of spike frequency in
ommatidia. Lower curve: responses to rectangular pattern, upper curve: responses to small spot of light.
The differences between the two curves illustrate that lateral inhibition enhances the response on the
light side of an edge and depresses the response on the dark side of an edge. Mutual inhibition plays a
role in contrast enhancement and feature extraction.
The Cafe Wall illusion
The Cafe Wall illusion
The original of the Café Wall, St Michael's Hill, Bristol.
The Cafe Wall illusion
The part of the line indicated by an violet circle is surrounded by a large white region. These areas will
be dimmed in the retina. The part of the line indicated by a orange circle is surrounded by dark regions,
and will be slightly brightened in the retina. The result is that each line acquires a faint diagonal striping,
which develops into converging slopes.
http://www.positscience.com/brain-resources/brain-teasers/cafe-wall-illusion
Perception
1. Detection (receptor threshold, behavior threshold)
P – pupil
FP – fixation point
M - monochromators
S – shutter
L - lamp
Setup for measuring minimal energy to induce visual response. The eye at the pupil P fixates the red point FP
and observes the test field formed by the lens FL and the diaphragm D. The light for this field comes from the
lamp L through the neutral filter F and wedge W, through the double monochromator M 1,M2 and is controlled by
the shutter S. From: Selig Hecht, Simon Shaleri Maurice Henri Pirenne. Energy, Quanta and Vision. The
Journal of General Physiology, Vol 25, 819-840 (1942)
Conclusions:
- Single photon is adequate for stimulating a single photoreceptor in human retina (it
was known before).
- Simultaneous activation of 7 (5 - 14) receptors is necessary to perceive that
stimulation has occured.
Perception
Continuum
Exponent
(a)
Stimulus condition
Loudness
0.67
Sound pressure of
3000 Hz tone
Brightness
0.5
Point source
Brightness
1
Point source briefly
flashed
Taste
1.3
Sucrose
Taste
1.4
Salt
Taste
0.8
Saccharine
Cold,
1
Metal contact on arm
Warmth
1.6
Metal contact on arm
Warmth
0.7
Irradiation of skin,
large area
Thermal pain
1
Radiant heat on skin
Pressure on palm
1.1
Static force on skin
Muscle force
1.7
Static contractions
Heaviness
1.45
Lifted weights
Electric shock
3.5
Current through
fingers
Angular
acceleration
1.4
5 s rotation
Duration
1.1
White noise stimuli
2. Magnitude estimation
Weber – Fechner law
p  k log( S / S0 )
p – perception
k – constant to be determined experimentally
S – stimulus
S0- threshold stimulus
Stevens’ power law
p  k ( S  S0 )
a - exponent
a
Weber – Fechner law vs. Stevens’ law
6
x
5
0.7
4
y(x)
ln(x)
3
2
1
0
2
3
4
5
6
x
7
8
9
10
Perception
3. Spatial discrimination
Two – point discrimination in various body parts. The best discrimination occurs at the finger tips,
lips and tongue.
Perception
4. Quality discrimination
Analytic
Synthetic
Perception
5. Pattern recognition
Gestalt psychology is a theory of mind
and brain. Its operational principle is
that the brain is holistic, parallel, and
analog, with self-organizing tendencies.
The principle maintains that the human
eye sees objects in their entirety before
perceiving their individual parts,
suggesting the whole is greater than the
sum of its parts.