Sensation & Perception

What is Sensation? Passively receiving information through sensory inputs. Cells that detect physical energy are located in sense organs Eyes Ears Nose Tongue Skin Internal body tissue

What is Perception? The interpretation of sensory signals.

Example? Hearing your ringtone = sensation Recognizing the song = perception Hearing a voice = sensation Recognizing your mother’s voice = perception

How Many Senses Do We Have? More than five, though scientists disagree on how many. Vision (eyes) Hearing (ears) Taste (tongue) Touch (skin) Smell (nose)

How Many Senses Do We Have? BUT WAIT! THERE’S MORE! Skin can also sense heat, cold, pain, itching, tingling Ear also contains receptors for balance Skeletal muscles contain receptors for a sense of bodily movement.

Why are Senses Important? Help us survive Even pain is a crucial part of our evolutionary heritage Alerts us to illness and injury But they also… Entertain us Amuse us Soothe us Inspire us

Sensation Sensation begins with sense receptors Cells located in sense organs Receptors detect appropriate stimulus—light, pressure, or chemical molecules—and convert the energy into electrical impulses that travel along nerves to brain.

Think of it like this… Sense receptors are like military scouts who scan terrain for activity. Scouts can’t make decisions on their own. Must transmit what they see to field officers (neurons). Field officers report to generals at the command center (brain). Brain cells responsible for analyzing reports (stimulus), combining information brought in by different scouts (senses), and deciding what it all means.

Think of it like this… “Field officers”—sense receptors—all use the same form of communication, a neural impulse, or pulse of electrical energy. Sensory Receptors Neurons Brain

What if we could sense everything? Life would be a headache. We can only take in a window of what is out there. Known as the study of psychophysics Studies how the strength or intensity of a stimulus affects the strength of sensation

Measuring the Senses

Absolute Threshold The smallest amount of energy that a person can detect reliably (50% of the time) Not really absolute: people detect borderline signals on some occasions and not others. http://www.youtube.com/watch?v=4G60hM1W_mk http://www.youtube.com/watch?v=wVhiezByMSU

Absolute Threshold Absolute Threshold Intensity No No No Yes Yes Observer’s Response Detected Tell when you (the observer) detect the light.

Absolute Thresholds for Humans SENSE STIMULUS RECEPTORS THRESHOLD Vision Electromagnetic Energy Rods & Cones in the retina A candle flame viewed from a distance of about 30 miles on a dark night Hearing Sound Waves Hair cells of the inner ear The ticking of a watch from about 20 feet away in a quiet room Smell Chemical substances in the air Receptor cells in the nose About one drop of perfume diffused throughout a small house Taste Chemical substances in saliva Taste buds on the tongue About 1 teaspoon of sugar dissolved in 2 gallons of water Touch Pressure on the skin Nerve endings in the skin The wing of a fly falling on a cheek from a distance of about 0.4 inches

Difference Thresholds The smallest difference in stimulation that a person can detect reliably (50% of the time) The just noticeable difference Ex: Comparison of the weight of two blocks, brightness of two lights, or saltiness of two liquids. http://www.youtube.com/watch?v=hyEoVN97J1c

Weber’s Law Idea that, to perceive a difference between two stimuli, they must differ by a constant percentage; not a constant amount.

Weber’s Law When comparing A and B, the difference threshold will depend on the intensity or size of A. The larger or more intense A is, the greater the change must be before you can detect a difference.

Signal-Detection Theory Predicts how and when we detect the presence of a faint stimulus (signal). SDT assumes there is no single absolute threshold Detection depends on… Person’s experience Expectations Motivation Level of fatigue

Signal-Detection Theory Measurements for any given individual may be affected by the person’s general tendency, when uncertain, to respond, “Yes, I noticed a signal (or difference)” or “No, I didn’t notice anything.” Some people are habitual yea-sayers, others nay-sayers

Sensory Adaptation Diminished sensitivity as a consequence of constant stimulation. Ex: Put a band aid on and after a while, you don’t sense it.

Sensory Adaptation Hold your hand over one eye and stare at the dot in the middle of the circle. Gradual change from light to dark does not provide enough contrast for visual receptors firing at a steady rate.

Sensory Deprivation Some become disoriented, confused, restless, or grouchy. Some enjoy limited periods of deprivation, and some perceptual and intellectual abilities actually improve. http://www.youtube.com/watch?v=dtZNjzeShYw

Selective Attention Focusing conscious awareness on a particular stimulus to the exclusion of others. The ability to focus on one stimulus at a time. Allows a person to function in a world filled with many stimuli. People with ADD have trouble doing this.

Read this. Now read it again.

Selective Attention Example: Cocktail Party Effect Ability to listen to one voice among many. To pay attention despite many distraction.

Inattentional Blindness The inability to see an object or a person in our midst. Is Google Glass dangerous? https://www.youtube.com/watch?v=Yu3zlWVCcjY