PSY.LECT4 sensation and perception 2 4medicine

Sensation and PerceptionPart II

Dr. Perjan Hashim Taha Psychiatrist M.B.Ch.B. Msc.C.A.P. F.I.C.M.S.(Psych) University of Duhok/Faculty of Medical sciences School of Medicine
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Visual Processing in the Brain

After being processed in the thalamus and different areas of the brain, visual signals reach the primary visual cortex in the occipital lobe of the brain’s cerebrum. - highly specialized cells called feature detectors respond to these visual signals in the primary visual cortex. - Feature detectors are neurons that respond to specific features of the environment, such as lines and edges. From the visual cortex, visual signals often travel on to other parts of the brain, where more processing occurs. Cells deeper down the visual processing pathway (visual association area) are even more specialized than those in the visual cortex. Perception occurs when a large number of neurons in different parts of the brain activate. These neurons may respond to various features of the perceived object such as edges, angles, shapes, movement, brightness, and texture. Dr.Perjan
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Perception

is the organization, identification and interpretation of sensory information in order to represent and understand the environment Perception depends on complex functions of the nervous system, but subjectively seems mostly effortless because this processing happens outside conscious awareness The perceptual systems of the brain enable individuals to see the world around them as stable, even though the sensory information may be incomplete and rapidly varying
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What is this?
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so
person's concept and expectations (knowledge) influence perception.
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Perception

What is this?

So this rubin vase can be perceived in diff. views

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Perceptual constancy

Perceptual constancy is the ability of perceptual systems to recognize the same object from widely varying sensory inputs For example, individual people can be recognized from views, such as frontal and profile, which form very different shapes on the retina. A coin looked at face-on makes a circular image on the retina, but when held at angle it makes an different image is a tendency to maintain constancy (of size, color, and shape) in the perception of stimuli even though the stimuli have changed
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Perceptual grouping
The principles of grouping (or Gestalt laws of grouping) are a set of principles in psychology, first proposed by Gestalt psychologist to explain how humans naturally perceive objects as organized patterns and objects. These principles: The principle of proximity states that perception tends to group stimuli that are close together as part of the same object, and stimuli that are far apart as two separate objects.
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The nine squares above are placed without proximity. They are perceived as separate shapes.

When the squares are given close proximity, unity occurs. While they continue to be separate shapes, they are now perceived as one group.
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The principle of similarity states that, stimuli that physically resemble each other are perceived as part of the same object, and stimuli that are different as part of a different object.
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The principle of closure refers to the mind’s tendency to see complete figures or forms even if a picture is incomplete, Dr.Perjan
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or even if part of the information needed to make a complete picture is missing, in our mind it will be completed.

Although the panda above is not complete, enough is present for the eye to complete the shape. When the viewer's perception completes a shape, closure occurs.
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Color Vision
Objects in the world seem to be brightly colored, but they actually have no color at all.Red cars, green leaves, and blue shirts certainly exist—but their color is a psychological experience. Objects only produce or reflect light of different wavelengths and amplitudes. Our eyes and brains then convert this light information to experiences of color. Color vision happens because of two different processes, which occur in sequence: The first process occurs in the retina and is explained by the trichromatic theory. The second process occurs in retinal ganglion cells and in cells in the thalamus and visual cortex. The opponent process theory explains this process. Dr.Perjan
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Trichromatic Theory

Young (1802) & von Helmholtz (1852) both proposed that the eye detects 3 primary colors: red, blue, & green All other colors can be derived by combining these three.
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The Trichromatic Theory

Thomas Young and Hermann von Helmholtz proposed the trichromatic theory, or Young-Helmholtz theory. This theory states that the retina contains three types of cones, which respond to light of three different wavelengths, corresponding to red, green, or blue. Activation of these cones in different combinations and to different degrees results in the perception of other colors.
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The Trichromatic theory accounts for color blindness, a hereditary condition that affects a person’s ability to distinguish between colors. Most color-blind people are dichromats, which means they are sensitive to only two of the three wavelengths of light. Dichromats are usually insensitive either to red or green, but sometimes they cannot see blue. Dr.Perjan
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Test of Color Deficiency

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The Opponent Process Theory
Ewald Hering proposed the opponent process theory. According to this theory, the visual system has receptors that react in opposite ways to three pairs of colors. The three pairs of colors are: 1) red versus green, 2) blue versus yellow, 3) black versus white.
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Some receptors are activated by wavelengths corresponding to red light and are turned off by wavelengths corresponding to green light. Other receptors are activated by yellow light and turned off by blue light. Still others respond oppositely to black and white.
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Opponent process theory explains why most people perceive four primary colors: red, green, blue, and yellow. If trichromatic theory alone fully explained color vision, people would perceive only three primary colors, and all other colors would be combinations of these three colors. However, most people think of yellow as primary rather than as a mixture of colors.

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Afterimages

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* is visual sensation that continues after the stimulus ends.

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* Now just concentrate on the (plus sign +) in the following image for 60 seconds Or count till 60 and then look at other area


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* Now just concentrate on the (yellow circle ) without closing your eyes for 60 seconds and then look inside the square

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Why this happen?

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Why this happen?When our eyes are exposed to a hue for a prolonged period, the rods & cones become fatigued. You might notice this if you are reading something on colored paper, and then look away—you often see the inverse, or complement, of the image Dr.Perjan
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Touch

The sense of touch encompasses pressure, pain, cold, and warmth. Pressure has specific receptors. Touch have different thresholds in different parts of body.
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THE PERCEPTION OF PAIN
Pain is an unpleasant yet important function for survival: warning system (but not all pain is needed for survival). There are two different pathways to the brain on which pain can travel - information brought from free nerve endings in the skin to the brain : 1) Fast pathways - registers localized pain (usually sharp pain) and sends the information to the cortex in a fraction of a second.

2) Slow pathways - sends information through the limbic system which takes about 1-2 seconds longer than directly to the cortex (longer lasting, aching/burning).
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Factors in Pain Perception – not an automatic result of stimulation: 1) Expectations - research shown that our expectations about how much something will hurt can effect our perception.2) Personality - people with negative types of personalities often have more pain.3) Mood - bad moods, angry, unhappy …etc, can lead to the experience of increased pain. Dr.Perjan
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So, it seems that our brains can: regulate, control, determine, and even produce pain.

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THEORIES OF PAIN PERCEPTION

* Gate Control Theory (Melzack & Walls, 1965) - incoming pain must pass through a "gate" located in the spinal cord which determines what information about pain will be sent to the brain. So, it can be opened to allow pain through or closed to prevent pain from being perceived. The Gate-actually a neural network controlled by the brain located in an area of the spinal cord called the Substansia Gelatinosa.
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There are two types of nerve fibers in this area: a) Large - sends fast signals and can prevent pain by closing the gate. b) Small - sends slower signals which open the gate. So - when pain occurs it is because the large fibers are off and the small are on, opening the gate. Since the gate is controlled by the brain, the factors discussed earlier (expectations, mood, personality) influence the functioning of the gate.
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Contradiction to Gate Control Theory:
endorphins - the body's own pain killers (morphine-like). May explain acupuncture, pain tolerance during last two weeks of pregnancy,…etc.BUT- endorphins may work with the gate control theory - maybe pain is perceived, endorphins are released, so the brain no longer needs the signals and closes the gate. Dr.Perjan
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PHANTOM LIMBS

Ability to feel pain, pressure, temperature, and many other types of sensations including pain in a limb that does not exist (either amputated or born without). Explanations: 1) The neuroma explanation 2) The spinal cord explanation 3) The brain explanation. 4) The hardwired explanation.
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Explanations:

1) the neuroma explanation - remaining nerves in the stump grow into nodules (neuromas) at the end of the stump continue to fire signals. 2) the spinal cord explanation - neurons in the spinal cord that are no longer receiving information from the lost appendage continue to send information to the brain.
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3) the brain explanation - signals in the somatosensory circuits of the brain change when the limb is lost which produce the phantom...the brain compensates for the loss or altered signals. 4) the hardwired explanation - we may have a biological makeup to be born with all of our appendages. So, when we are born and lose one limb, the nerves are still there and are still going to send the information
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Hearing

Hearing depends on sound waves. Sound has three features: loudness, pitch, and timbre, which depend respectively on wave amplitude, frequency, and complexity.
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What We Hear
LoudnessThe dimension of auditory experience related to the intensity of a pressure wave.PitchThe dimension of auditory experience related to the frequency of a pressure wave.Timbre (pronounced “TAM-bur”)The distinguishing quality of sound; the dimension of auditory experience related to the complexity of the pressure wave. Dr.Perjan
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Structures of the Ear

The ear comprises the outer ear, the middle ear, and the inner ear. These parts contain the pinna, the eardrum, ossicles, oval window, cochlea, and cilia. Neurons in the ear form the auditory nerve, which sends impulses from the ear to the brain. The thalamus and auditory cortex receive auditory information.
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Structures of the Ear

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