Experiencing the World Sensation Experiencing the World

Sensation Sensation a process by which our sensory receptors and nervous system receive and represent stimulus energy Perception a process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events

Sensation & Perception Causally related with perceptions organizing sensations

Sensation Bottom-Up Processing Top-Down Processing analysis that begins with the sense receptors and works up to the brain’s integration of sensory information Top-Down Processing information processing guided by higher-level mental processes as when we construct perceptions drawing on our experience and expectations

Sensation- Basic Principles Psychophysics - study of the relationship between physical characteristics of stimuli and our psychological experience of them Lumens of light - brightness Size of air wave - loudness Pressure- weight Chemical compounds - sweetness

Sensation & reality Objective reality is very different than the way we sense and perceive it No colors, tastes, smells, etc. in natural world Just stimulus energy of various sorts We process this energy and ‘psychologize’ it We transform it into color, tastes, smells that don’t exist in natural world

The world is not always as we sense it...

Reaction Paper II: Sensation Describe what is meant by ‘the world is not as you sense it.’ What is your reaction to this? How do you think this may change the way you view the world? PLEASE TURN THESE IN AFTER CLASS!

Sensation- Thresholds Absolute Threshold minimum stimulation needed to detect a particular stimulus usually defined as the stimulus needed for detection 50% of the time

Sensation- Thresholds Difference Threshold minimum difference between two stimuli that a subject can detect 50% of the time just noticeable difference (JND) increases with magnitude

Sensation- Thresholds Signal Detection Theory predicts how and when we detect the presence of a faint stimulus (signal) amid background stimulation (noise) assumes that there is no single absolute threshold detection depends partly on person’s experience expectations motivation level of fatigue

Sensation- Thresholds 25 50 75 100 Low Absolute threshold Medium Intensity of stimulus Percentage of correct detections Subliminal stimuli When stimuli are detectable less than 50% of the time (below one’s absolute threshold) they are “subliminal”. Threshold

Sensation- Thresholds Weber’s Law- to perceive a difference between two stimuli, they must differ by a constant proportion light intensity- 8% weight- 2% tone frequency- 0.3% 100 candles in a room need 8 more to see a difference

Sensation- Thresholds Sensory adaptation- diminished sensitivity to constant stimulation

Spectrum of Electromagnetic Energy Vision Light is energy

Vision Transduction - conversion of one form of energy to another Electromagnetic to electrical-chemical

Vision- Physical Properties of Waves Wavelength - distance from peak to peak Determines color (Hue)

Structures of the eye Cornea - outermost covering of eye Begins process of focusing Pupil- adjustable opening in center Iris- a ring of muscle = colored portion controls size of pupil opening Lens- transparent & changes shape to focus images on retina Accommodation

Vision

Vision Retina inner surface of eye light sensitive layers of neurons begins visual information processing transduction

Retina’s Reaction to Light Cones (6 million) near center of retina (fovea) fine detail and color vision daylight or well-lit conditions Rods (120 million) peripheral retina detect black, white and gray twilight or low light (video)

Retina’s Reaction to Light Retina converges out the eye through... Optic nerve- nerve that carries neural signals from the retina to brain Blind Spot- optic nerve leaves the eye with no receptor cells DEMO (close left eye look at y) Y X

Eye

Pathways from the Eyes to the Visual Cortex

Visual Information Processing Feature Detectors - neurons in the visual cortex respond to specific features shape angle movement Stimulus Cell’s responses

Visual Information Processing Parallel Processing-simultaneous processing of several dimensions through multiple pathways color motion form depth

Visual Information Processing Scene Retinal processing: Receptor rods and conesbipolar cells  ganglion cells Feature detection: Brain’s detector cells respond to elementary features-bars, edges, or gradients of light Abstraction: Brain’s higher-level cells respond to combined information from feature-detector cells Recognition: Brain matches the constructed image with stored images

Flexiblity Visual system flexible Rapid adaptation to changing stimulus energy Inverted vision video Why do you think this flexibility is part of our visual system?

Other senses Audition Touch Taste Smell Pain See text for this information

Sensation Summary Processing stimulus energies Basic principles Reality Thresholds Visual processing