Sensation and Perception

Sensation Sensation: The process of detecting a stimulus (something that attracts the attention of a sensory organ) the stimulation of sensory receptors and the transmission of sensory information to the central nervous system Five Traditional Senses: Vision Hearing Touch Taste Smell

Sensation Sensory Receptors: located in the sensory organs (eyes, ears, nose, tongue, hands) Definition cells that convert physical energy in the environment or the body to electrical energy that can be transmitted as nerve impulses to the brain

Sensation Five Sensory Receptors: Temperature Pressure Pain Balance Motion

Perception Perception: process by which the brain organizes & interprets sensory information using sensory information to form a meaningful pattern final, organized, meaningful experience of sensory information An example: Have you ever started the car and had to quickly turn down the volume on the radio from where it was set last time you were in the car? The level of energy (I.e., loudness) of the radio hasn’t changed (the volume know remains in the same place as when you last had it on), but your perception of the loudness has changed drastically!

The Process

Thresholds Definition: minimum amount of any given sensation that has to be present for us to notice it Ticking of a watch from 20 ft away Absolute Threshold: minimum amount of a stimulus that is necessary for us to notice it 50% of the time 1 drop of perfume in a small house Just Noticeable Difference: (Difference Threshold) Smallest amount of difference in amount of stimulation that a specific sense can detect (difference in shades of two colors) Smallest difference in the shades of red your eye can see

Sensory Adaptation Sensory Adaptation: process by which we become less aware of weak stimuli if a stimulus is unchanging, we become desensitized to it We adapt to lying on a beach by becoming less aware of weak stimuli like the sounds of the ocean We adapt to living near a highway by becoming less aware of the sounds of traffic

Sensory Overload Definition: Overstimulation of the senses. Can use selective attention to reduce sensory overload Selective Attention focusing of attention on selected aspects of the environment and the blocking out of others

“Our Visible Spectrum” Light “Our Visible Spectrum” Red Orange Yellow Green Blue Indigo Violet Hue determines color Depends on length of the distance from one peak to the next on the wave 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.

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.

The Eye Retina Neural tissue lining the back of the eyeball’s interior, which contains the receptors for vision. Rods Visual receptors that respond to dim light. Cones Visual receptors involved in color vision. Most humans have 3 types of cones.

The Ear Loudness Pitch Timbre The dimension of auditory experience related to the intensity of a pressure wave. Pitch The dimension of auditory experience related to the frequency of a pressure wave. Timbre The distinguishing quality of sound; the dimension of auditory experience related to the complexity of the pressure wave.

The Ear

The Ear Auditory Localization: Sounds from different directions are not identical as they arrive at left and right ears Loudness Timing Phase The brain calculates a sound’s location by using these differences.

The Ear Three theories on how we perceive sound: Frequency Theory Neural impulses are stimulated more with higher frequencies of air waves More plausible for small frequencies, rather than high frequencies because we can hear freqs higher than the maximum rate of neural firing (1,000 neurons a second) Place Theory Different frequencies of air waves activate different places along the basilar membrane Volley Theory Neurons fire out of sequence to add up to a certain Hz

Smell Olfaction Lock-and-key Detects molecules in the air Olfactory receptors (i.e., the locks) are built so that only molecules (the keys) with particular shapes will fit in particular receptors Receptors send neural signals to the brain, passing the thalamus (memory) and the limbic system (emotions) along the way This is why odors often trigger emotional memories

Taste Detects molecules of substances that have dissolved in saliva Taste Buds Clusters of hair-like receptor cells Within each bud is a cluster of 50 to 150 receptor cells We have about 10,000 (most on tongue) Four types: sweet, sour, salty & bitter

taste The Process Sense of taste combines with the sense of smell to produce perception of flavor of food Research suggests that neural impulses for both senses converge to some degree in brain area associated with the perception of flavor When the sense of smell is blocked, we have a harder time detecting most flavors

Skin Senses Touch Skin is the body’s largest sensory organ Millions of skin receptors mix and match to produce specific perception Four basic types of sensations Pressure, warmth, cold, and pain

Skin Senses Temperature Two separate sensory systems – one for signaling warmth and the other for signaling cold Also have distinct spots on the skin that register only warmth or cold If you activate both at the same time, the person perceives ‘hot’!

Skin Senses Pain Pain serves a function – it warns us of impending danger Endorphins Neurotransmitters in the brain that have a pain-killing effect Gate-control theory Pain impulses can be inhibited by closing of neural gates in the spinal cord

Sensitivity to touch

Body Senses Kinesthetic sense Vestibular sense Provides info about position of joints, muscles, limbs Gives us control over body movements Vestibular sense Provides info about body’s orientation relative to gravity and head’s position in space Helps us maintain balance Relies on semicircular canals in the inner ear

Influences on Perception Our needs affect our perception because we are more likely to perceive something we need Our beliefs can affect what we perceive Emotions, such as fear, can influence perceptions of sensory information All are influenced by our culture. Expectations based on our previous experiences influence how we perceive the world.

Perceptual Set What you see in the centre figures depends on the order in which you look at the figures: If you scan from the left, see an old woman If you scan from the right, see a woman’s figure

Context Effects The same physical stimulus can be interpreted differently We use other cues in the situation to resolve ambiguities Is this the letter B or the number 13?

Rules of Perceptual Organization Gestalt Principles of Vision: notes the various ways people make sense of sensory information through: Figure-Ground The recognition of objects against a background What we perceive as the object & perceive as the background influence our perception

Rules of Perceptual Organization Proximity Grouping together visual & auditory stimulus which are near to one another Marks near one another tend to be grouped together What do you see? - 3 rows of dashes or 36 dashes Similarity Tendency to group elements together that look alike Marks that look alike tend to be grouped together What do you see? - 3 columns of red or a 4 x 6 pattern

Rules of Perceptual Organization Closure We tend to fill in gaps in what your senses tell you Continuity Marks that tend to fall along a smooth curve or a straight line tend to be grouped together People prefer to see smooth continuous patterns not disrupting ones

Depth and Distance Binocular Cues: Visual cues to depth or distance that require the use of both eyes.

Depth and Distance Convergence: Turning inward of the eyes, which occurs when they focus on a nearby object. Retinal Disparity: The slight difference in lateral separation between two objects as seen by the left eye and the right eye.

Depth and Distance Monocular Cues: visual cues to depth or distance that can be used by one eye alone. Cues create the illusion of three dimensions or depth on two dimensional or flat surfaces Cause certain objects to appear more distant than others

Visual Constancies The accurate perception of objects as stable or unchanged despite changes in the sensory patterns they produce. Size constancy Color constancy Brightness constancy Shape constancy

Size Constancy the tendency to perceive an object as being of one size no matter how far away the object is

Color Constancy the tendency to perceive an object as keeping their color even though different light may change the appearance of their color

Brightness Constancy the tendency to perceive an object as being equally bright even when the intensity of the light around it changes

Shape Constancy the knowledge that an item has only one shape no matter what angle you view it from even though these images cast shadows of different shapes, we still see the quarter as round

Visual Illusions Illusions are valuable in understanding perception because they are systematic errors that reveal our experiences Illusions provide hints about perceptual strategies. In the Ponzo Illusion (above) side lines seem to converge and top line seems farther away, but the retinal images of the red lines are equal! In the Muller-Lyer illusion (above) we tend to perceive the line on the right as slightly longer than the one on the left.