Transcript Receptors
Sensation and Perception 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 How Are the Senses Alike? How Are They Different? 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 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 Pain receptors Pain over body Kinesthetic Body position & or balance Vestibular 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 Pain receptors Pain over body Kinesthetic Body position & or balance Vestibular 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 Pain receptors Pain over body Kinesthetic Body position & or balance Vestibular 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 Pain receptors Pain over body Kinesthetic Body position & or balance Vestibular 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 Pain receptors Pain over body Kinesthetic Body position & or balance Vestibular 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 Pain receptors Pain over body Kinesthetic Body position & or balance Vestibular 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 Pain receptors Pain over body Kinesthetic Body position & or balance Vestibular Semi-circular canals; joints, tendons Hair cells; specialized neurons Body position The Anatomy of Visual Sensation 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 dim light but not colors Cones – Sensitive to colors but not dim light Fovea – Area of sharpest vision in the retina 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 Transduction of Light in the Retina The Anatomy of Visual Sensation • Visual cortex – Part of the brain – the occipital cortex – where visual sensations are processed Neural Pathways in the Human Visual System 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 Color Blindness Perception 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 Reversible Figures Reversible Figure 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 Distal Stimulus Proximal Stimulus Images Projected on the Retina 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 Figure / Ground Proximity Similarity Continuity Common Fate Closure Goodness of Form or Pragnanz = Images Projected on the Retina Proximal Stimulus 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 Proximal Stimulus Distal Stimulus 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 Linear Perspective A B Which box is bigger, A or B? Moon Illusion Final Thoughts • Visual system is exceptionally good at analyzing the outside world – i.e., perception is a faithful representation of the distal stimulus • Understanding how the visual system is tricked (i.e., by studying common illusions) helps us to understand how it works