PSY.LECT3 sensation and perception 1 4th class

Sensation and PerceptionPart I

Dr. Perjan Hashim Taha Psychiatrist M.B.Ch.B. Msc.C.A.P. F.I.C.M.S.(Psych) Psychiatry Department
Dr.Perjan
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Sensations can be defined as the passive process of bringing information from the outside world into the body and to the brain. - The detection of physical energy reflected by physical objects. It occurs when energy in the external environment or the body stimulates receptors in the sense organs. Perception can be defined as the active process of selecting, organizing, and interpreting the information brought to the brain by the senses.
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A) HOW THEY WORK TOGETHER?

1) Sensation occurs: a) Sensory organs absorb energy from a physical stimulus in the environment. b) Sensory receptors convert this energy into neural impulses and send them to the brain. 2) Perception follows: The brain organizes the information and translates it into something meaningful.
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Sensation & Perception Processes

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Sensory receptors

Sensory receptors are cells that are specialized for the task of transduction, or converting physical energy into neural impulses. Types: Rods and cones in the retina, which transduce light. Cilia in the ear, which transduce sound Pressure, vibration, heat, and pain receptors in the skin Chemical receptors in the nasal cavities and mouth Muscle spindles
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Sensory systems
1- visual system for sight. 2- auditory system for hearing 3- tactile system for touch. 4- olfactory system for smell. 5- gustatory system for taste. -The kinesthetic sense: provide information about movement, posture, and orientation. -The Vestibular senses: provide information about balance and movement.
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How do we know what information is important and should be focused on?

1) Selective Attention – The focusing of attention on selected aspects of the environment and the blocking out of others. e.g. students in class should focus on what the teachers are saying and the overheads being presented (and not on what is going outside) . Students walking by the classroom may focus on people in the room, his mobile phones …etc, and not the same thing the students in the class. Dr.Perjan
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2) Perceptual Expectancy - how we perceive the world is a function of our past experiences, culture, and biological makeup.
e.g. when an American, look at a highway, he/she expect to see cars, trucks, etc, NOT airplanes. But someone from a different country with different experiences and history may not have any idea what to expect and thus be surprised when they see cars go driving by.
ALL OF THIS IS CALLED Psychophysics.
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Psychophysics can be defined as, the study of how physical stimuli are translated into psychological experience.
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Measuring the Senses

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1) Absolute ThresholdThe minimum amount of energy that can be detected. Or the minimum amount of stimulation required for a person to detect the stimulus 50 percent of the time.Or a dividing line between detectable energy and not.
E.g. the weakest light that can be discriminated in the darkness
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Absolute Sensory Thresholds Approximate minimum stimuli for various senses Vision: A single candle flame from 30 miles on a dark, clear night Hearing: The tick of a clock from 20 feet in total quiet Smell: 1 drop of perfume diffused in a 6 rooms Touch: The wing of a bee on your cheek, dropped from 1 cm Taste: 1 tea spoon sugar in 2 galons water
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2) Difference ThresholdThe minimum amount of stimulus intensity change needed to produce a noticeable change.sometimes called the just noticeable difference (JND), and it depends on the strength of the stimulus. The greater the intensity (ex., weight) of a stimulus, the greater the change needed to produce a noticeable change.
E.g. when you pick up a 5 kg weight, and then a 10 kg weight, you can feel a big difference between the two. but , when you pick up 100 mg, and then 105 mg, it is much more difficult to feel the difference
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3) Signal-Detection Theory: The sensitivity to sensory stimuli also depends on: individual and contextual variations such as fatigue, expectancy, and urgency of the moment.
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e.g. in an experiment if light of different intensities is presented and asking the observer to report “Yes, I see the light” or “No, I don’t”.Observers may sometimes say “Yes, I detect the light” when actually they don't but only think they see it. Dr.Perjan
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Sensory Adaptation& Deprivation

Sensory adaptation is the decrease in sensitivity to an unchanging stimulus.When people walk into a restaurant, they probably notice food smells right away  as they sit in the restaurant, the smells gradually become less noticeable. This phenomenon occurs because of sensory adaptation. The smells don’t disappear—the people just become less sensitive to them. Sensory deprivationThe absence of normal levels of sensory stimulation Dr.Perjan
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SIGHT/VISION

Researchers have studied vision more thoroughly than the other senses. Because people need sight to perform most daily activities, the sense of sight has evolved to be highly sophisticated.
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What We See:

Hue Visual experience specified by color names and related to the wavelength of light. Brightness Lightness and luminance; the visual experience related to the amount of light emitted from or reflected by an object. Saturation Vividness or purity of color; the visual experience related to the complexity of light waves.
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What We See

Hue Brightness Saturation
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The visual system works on perceiving light waves  Vision, would not exist without the presence of light.Light is electromagnetic radiation that travels in the form of waves. Light is emitted from the sun, stars, fire, and light bulbs. Most other objects just reflect light.Light waves vary in their length and amplitude. Dr.Perjan
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People experience light as having three features: color, brightness, and saturation. These three types of experiences come from three corresponding characteristics of light waves:
1- The color or hue of light depends on its wavelength, the distance between the peaks of its waves. also referred to as frequency, (since the longer a wave, quickly it occurs) - affects color perception (ex., red=approx 700nm, yellow approx 600nm).
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2- Brightness of light is related to intensity or the amount of light an object emits or reflects. It depends on light wave amplitude, the height of light waves. It is also somewhat influenced by wavelength. Yellow light tends to look brighter than reds or blues.
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3- Saturation or colorfulness depends on light complexity, the range of wavelengths in light. The color of a single wavelength is pure spectral color. Such lights are called fully saturated. Outside a laboratory, light is rarely pure or of a single wavelength. - Light is usually a mixture of several different wavelengths. - The greater number of spectral colors in a light, the lower the saturation.

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Structure of the EYE:

Cornea Protects eye and bends light toward lens. Lens Focuses on objects by changing shape. Iris Controls amount of light that gets into eye. Pupil Widens or dilates to let in more light.
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RetinaNeural tissue lining the back of the eyeball’s interior, which contains the receptors for vision.RodsVisual receptors that respond to dim light.ConesVisual receptors involved in color vision. Most humans have 3 types of cones. Dr.Perjan
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Structures of the Retina

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Rods and cones connect via synapses to bipolar neurons, which then connect to other neurons called ganglion cells. The axons of all the ganglion cells in the retina come together to make up the optic nerve. The optic nerve connects to the eye at a spot in the retina called the optic disk. The optic disk is also called the blind spot because it has no rods or cones. Any image that falls on the blind spot disappears from view.
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Transmission of Visual Information

Visual information travels from the eye to the brain as follows: Light reflected from an object hits the retina’s rods and cones. Rods and cones send neural signals to the bipolar cells. Bipolar cells send signals to the ganglion cells. Ganglion cells send signals through the optic nerve to the brain. Bipolar and ganglion cells gather and compress information from a large number of rods and cones. Dr.Perjan
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Ganglion cell axons from the inner half of each eye cross over to the opposite half of the brain. This means that each half of the brain receives signals from both eyes. Signals from the eyes’ left sides go to the left side of the brain, and signals from the eyes’ right sides go to the right side of the brain. The diagram below illustrates this process. Dr.Perjan
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REFERENCE:

-PSYCHOLOGY, John W. Santrock, sixth edition, 2000.- Hilgard’s introduction to PSYCHOLOGY, R.L. Atkinson, R.C. Atkinson…et al. Dr.Perjan
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