Sensation: What is it?
• The process by which a stimulus in the environment produces a neural impulse that the brain interprets as a sound, image, odor, etc.
Transduction
• Transduction – Transformation of one form of energy into another – especially the transformation of stimulus information into nerve impulses
• Receptors –Specialized neurons that are activated by stimulation and transduce (convert) it into a nerve impulse
Transduction
• Sensory pathway – Bundles of neurons that carry information from the sense organs to the brain
Sensory Adaptation
• Sensory adaptation – Loss of responsiveness in receptor cells after stimulation has remained unchanged for a while
Thresholds
• Absolute threshold – Amount of stimulation necessary for a stimulus to be detected
• Difference threshold – Smallest amount by which a stimulus can be changed and the difference be detected (also called just noticeable difference – JND)
Thresholds
• Weber’s law – The JND is always large when the stimulus intensity is high, and small when the stimulus intensity is low
The senses all operate in much the same way, but each extracts different information
and sends it to its own specialized processing region
in the brain
How Are the Senses Alike? How Are They Different?
Sense Stimulus Sense Organ Receptor Sensation
Vision Light waves Eye Rods and cones
Color, brightness, motion
Hearing Sound waves Ear Hair cells Pitch, loudness
Skin Senses
External Contact
Skin Nerve endings Touch, warmth, cold
Smell Volatile Substances
Nose Hair cells Odors
Taste Soluble Substances
Tongue Taste buds Flavors
Pain Intense or Extreme Stimuli
Pain Fibers all over body
Pain receptors Pain
Kinesthetic & Vestibular
Body position or balance
Semi-circular canals; joints, tendons
Hair cells; specialized neurons
Body position
Sense Stimulus Sense Organ Receptor Sensation
Vision Light waves Eye Rods and cones
Color, brightness, motion
Hearing Sound waves Ear Hair cells Pitch, loudness
Skin Senses
External Contact
Skin Nerve endings Touch, warmth, cold
Smell Volatile Substances
Nose Hair cells Odors
Taste Soluble Substances
Tongue Taste buds Flavors
Pain Intense or Extreme Stimuli
Pain Fibers all over body
Pain receptors Pain
Kinesthetic & Vestibular
Body position or balance
Semi-circular canals; joints, tendons
Hair cells; specialized neurons
Body position
Sense Stimulus Sense Organ Receptor Sensation
Vision Light waves Eye Rods and cones
Color, brightness, motion
Hearing Sound waves Ear Hair cells Pitch, loudness
Skin Senses
External Contact
Skin Nerve endings Touch, warmth, cold
Smell Volatile Substances
Nose Hair cells Odors
Taste Soluble Substances
Tongue Taste buds Flavors
Pain Intense or Extreme Stimuli
Pain Fibers all over body
Pain receptors Pain
Kinesthetic & Vestibular
Body position or balance
Semi-circular canals; joints, tendons
Hair cells; specialized neurons
Body position
Sense Stimulus Sense Organ Receptor Sensation
Vision Light waves Eye Rods and cones
Color, brightness, motion
Hearing Sound waves Ear Hair cells Pitch, loudness
Skin Senses
External Contact
Skin Nerve endings Touch, warmth, cold
Smell Volatile Substances
Nose Hair cells Odors
Taste Soluble Substances
Tongue Taste buds Flavors
Pain Intense or Extreme Stimuli
Pain Fibers all over body
Pain receptors Pain
Kinesthetic & Vestibular
Body position or balance
Semi-circular canals; joints, tendons
Hair cells; specialized neurons
Body position
Sense Stimulus Sense Organ Receptor Sensation
Vision Light waves Eye Rods and cones
Color, brightness, motion
Hearing Sound waves Ear Hair cells Pitch, loudness
Skin Senses
External Contact
Skin Nerve endings Touch, warmth, cold
Smell Volatile Substances
Nose Hair cells Odors
Taste Soluble Substances
Tongue Taste buds Flavors
Pain Intense or Extreme Stimuli
Pain Fibers all over body
Pain receptors Pain
Kinesthetic & Vestibular
Body position or balance
Semi-circular canals; joints, tendons
Hair cells; specialized neurons
Body position
Sense Stimulus Sense Organ Receptor Sensation
Vision Light waves Eye Rods and cones
Color, brightness, motion
Hearing Sound waves Ear Hair cells Pitch, loudness
Skin Senses
External Contact
Skin Nerve endings Touch, warmth, cold
Smell Volatile Substances
Nose Hair cells Odors
Taste Soluble Substances
Tongue Taste buds Flavors
Pain Intense or Extreme Stimuli
Pain Fibers all over body
Pain receptors Pain
Kinesthetic & Vestibular
Body position or balance
Semi-circular canals; joints, tendons
Hair cells; specialized neurons
Body position
Sense Stimulus Sense Organ Receptor Sensation
Vision Light waves Eye Rods and cones
Color, brightness, motion
Hearing Sound waves Ear Hair cells Pitch, loudness
Skin Senses
External Contact
Skin Nerve endings Touch, warmth, cold
Smell Volatile Substances
Nose Hair cells Odors
Taste Soluble Substances
Tongue Taste buds Flavors
Pain Intense or Extreme Stimuli
Pain Fibers all over body
Pain receptors Pain
Kinesthetic & Vestibular
Body position or balance
Semi-circular canals; joints, tendons
Hair cells; specialized neurons
Body position
The Anatomy of Visual Sensation
Fovea – Area of sharpest vision in the retina
Retina – Light-sensitive layer at the back of the eyeball
Photoreceptors – Light-sensitive cells in the retina that convert light energy to neural impulses
Rods – Sensitive to dimlight but not colors
Cones – Sensitive tocolors but not dim light
The Anatomy of Visual Sensation
• Optic nerve – Bundle of neurons that carries visual information from the retina to the brain
Blind spot – Point where the optic nerve exits the eye and where there are no photoreceptors
The Anatomy of Visual Sensation
• Visual cortex –Part of the brain – the occipital cortex – where visual sensations are processed
How the Visual System Creates Color
Color –
Psychological sensation derived from the wavelength of visible light – color, itself, is not a property of the external world
How the Visual System Creates Color
• Electromagnetic spectrum – Entire range of electromagnetic energy, including radio waves, X-rays, microwaves, and visible light
• Visible spectrum – Tiny part of the electromagnetic spectrum to which our eyes are sensitive
Two Ways of Sensing Color
• Trichromatic theory– Three different types of cones that sense different
parts of the visible spectrum (i.e., red, green, & blue)– Explains initial stages of color vision
• Opponent Process Theory– From bipolar cells onward, visual system processes
color in either-or, complementary fashion (i.e., red vs green or blue vs yellow)
– Sensations of one color (e.g., red) inhibits sensation of its complementary color (i.e., green)
– Explains negative afterimages & color blindness
Afterimages
• Afterimages – Sensations that linger after the stimulus is removed
• In the following slide, fix your eyes on the dot in the center of the flag
Perception
• Same sensory input can give rise to very different perceptions
• Perceptual Set– Readiness to perceive stimuli in specific ways
• Reversible figures – drawing that is compatible with two different interpretations
Perception
• What is Perception?
– Active process in which we organize and interpret sensory information
• i.e., How we make sense of (or understand) what we see, hear, feel, taste, and smell
Object Perception
• Distal Stimulus – Stimuli that lie in the distance (i.e., in the
outside world)– Three-dimensional
• Proximal Stimulus– Stimulus that impinges directly onto your
sensory receptors (i.e., the retina)– Distorted and two-dimensional
Object Perception
• Feature Analysis – Analyze individual features and put them
together to form a whole
Bottom-Up Processing
• Start with the elements and progress to the whole
• Evidence– Hubel and Wiesel – cells in the cortex
operate as highly specialized feature detectors
Top-Down Processing
• Start with the whole and work towards the elements
– What we perceive is influenced by what we expect to see
• Context and prior experience are important
Object Perception• A number of Gestalt psychology principles can
help explain how we organize information in order to perceive a coherent whole
• Figure/Ground• Proximity• Similarity• Continuity• Common Fate• Closure• Goodness of Form or Pragnanz
Depth Perception
• Binocular Depth Cues– Binocular disparity – Each eye has a slightly different
view of the world (i.e., the distal stimulus)• The brain thus has two different BUT overlapping images of
the world• The difference between these two retinal (i.e., proximal)
images is used to compute distances to nearby objects
• For example:– Object at 25 feet – image projected to slightly different
locations on the right and left retina– Closer objects project images on locations that are
further apart on the right and left retina
Depth Perception
• Monocular Depth Cues– Occlusion– Relative Size– Familiar Size– Linear Perspective– Texture Gradient– Position relative to horizon
• Motion cues for Depth– Motion Paralax– Optic Flow
Size Perception
• The size of the retinal image depends on the distance of the object from the observer
– Further away = smaller retinal image
– Thus, to determine size, visual system must know how far away the object is