2013 Worth Publishers Unit 4 Sensation and Perception Psychophysics Copyright Allyn and Bacon 2006 Psychophysics is the scientific study of the relationship between stimuli and the sensations and perceptions evoked by these stimuli Sensation vs. Perception The process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment. The process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events. The brain receives input from the sensory organs. The brain makes sense out of the input from sensory organs. SensationPerception Copyright Allyn and Bacon 2006 Receptors Specialized neurons that are activated by stimulation and transduce (convert) it into a nerve impulse Transduction The process that converts physical energy, (such as light or sound waves,) into neural messagesthe only language the brain understands Sensory adaptation occurs due to. The loss of responsiveness in receptor cells after stimulation has remained unchanged for a while You feel the socks on your feet when you put them onbut not for long 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. We detect stuff based on our experiences, expectations, motivations & fatigue level. Absolute Threshold The smallest amount of stimulation necessary for a stimulus to be detected Normal Human Absolute Thresholds Vision: a candle flame on a clear, dark night = 30 miles Hearing: A ticking watch in a quiet room = 20 feet Taste: Tablespoons of sugar dissolved in two gallons of water = One Smell: Perfume diffused in a small house = one drop (1 part in 500 mil) Touch: Pressure of the wing of a fly falling on a cheek from.4 inch Difference Threshold / Just Noticeable Difference The smallest difference between two stimuli that can be detected as a difference For Example: Turning down stereo volumeyou may hear a differences, your sister with a different threshold may not If you can hear the difference, it exceeds your thresholdif she cant, it hasnt exceeded hers Webers Law For Example: If the TV volume is high, you have to turn it down a lot to make the difference noticeable The JND is always large when the stimulus intensity is high, and small when the stimulus intensity is low Webers Law In Practice If you make $5 an hour a 25 cent hour raise will be noticeable. But at $10 an hour you may need 50 cents to really realize a difference. In car sales, after the sale customer wont really notice $500 stereo. After drinking tea with lemon, a grapefruit will not taste as sour but after a roll, it will taste especially sour. After holding salty water in mouth, it will taste less salty, and drinking fresh water afterwards, it will taste sweet. Anatomy of the Eye Copyright Allyn and Bacon 2006 Photoreceptors Light sensitive cells (neurons), rods and cones, that absorb light energy and respond by creating neural impulses RODS Cells that detect black, white, and gray; Necessary for peripheral Vision Twilight vision CONES Retinal cells that detect colors Fine detail Function in daylight and well-lit conditions ConesRods Number6 million120 million Location in RetinaCenterPeriphery Sensitivity to dim light LowHigh Color sensitivityHighLow Detail sensitivityHighLow Parallel Processing The processing of several aspects of a problem simultaneously. Properties of Light Amplitude: the height of the peaks in a light wave determines brightness (larger amplitude = brighter colors) Frequency: the rate at which light waves move past a given point higher frequency = shorter wavelength determines hue (color)(short wavelength = blue, long = red) Theory that says we have three receptors for bluecolor: red, green blue Colors are sensed by three different types of cones sensitive to light in the red, blue, and green wavelengths Explains the earliest stage of color sensation Young-Helmholtz Trichromatic (3 color) Theory Opponent-Process Theory The red/green cells increase their firing when red is present and decrease it when green is present. The yellow/blue cells have an increased response to yellow and a decreased response to blue. Another type of cell increases its response rate for white light and decreases in the absence of light. Copyright Allyn and Bacon 2006 How Sound Waves Become Auditory Sensations Copyright Allyn and Bacon 2006 Sounds have only three sensory qualities: Pitch Loudness - Pitch Sensory characteristic of sound produced by the frequency of the sound waveLoudness Sensory characteristic of sound produced by the amplitude (intensity) of the sound waveMore intense sound waves produce louder sounds High Amplitude High Frequency 3. The cochlea vibrates and jostles fluid in the its tube. 4. The jostling causes bends hair cells that line the cochleas surface This triggers impulses in the adjacent auditory nerve (the nerve that sends messages to auditory cortex of temporal lobe) 16,000 Hair Cells!! Like wheat in a wheat field bending to varying levels of wind. Most Hearing Damage is a result of damage to these hair cells Think of Carpet? Loud noises v Damage to Hair Cells Ringing is Equivalent to Bleeding! Place Theory Different hairs vibrate in the cochlea when they different pitches. So some hairs vibrate when they hear high and other vibrate when they hear low pitches. Frequency Theory All the hairs vibrate but at different speeds. Position and Movement Vestibular Sense Sense of body orientation with respect to gravity Copyright Allyn and Bacon 2006 Tells how our bodies, especially the head, are postured. (Straight, leaning, upside down,) Also, how we are moving and how our motion is changing Closely associated with the inner ear and is carried to the brain on a branch of the auditory nerve Children develop their vestibular senses by swinging, spinning, twirling, and rolling around on the ground. C h ildren gravitate toward these movements naturally. Vestibular movement is in fact considered critical to brain development. Kinesthetic Sense Sense of body position and movement of body parts relative to each other Proprioception is another term that is often used interchangeably with Kinesthesia Figure 4.23 FIGURE 4.23 The skin senses include touch, pressure, pain, cold, and warmth. This drawing shows different forms the skin receptors can take. The only clearly specialized receptor is the Pacinian corpuscle, which is highly sensitive to pressure. Free nerve endings are receptors for pain and any of the other sensations. For reasons that are not clear, cold is sensed near the surface of the skin, and warmth is sensed deeper (Carlson, 1998). Figure 4.21 FIGURE 4.21 (a) Olfactory nerve fibers respond to gaseous molecules. Receptor cells are shown in cross section to the left. (b) Olfactory receptors are located in the upper nasal cavity. (c) On the right, an extreme close-up of an olfactory receptor shows fibers that sense gaseous molecules of various shapes. Figure 4.22 FIGURE 4.22 Receptors for taste: (a) The tongue is covered with small protrusions called papillae. (b) Most taste buds are found around the top edges of the tongue (shaded area). However, some are located elsewhere, including under the tongue. Stimulation of the central part of the tongue causes no taste sensations. All four primary taste sensations occur anywhere that taste buds exist. (c) An enlarged drawing shows that taste buds are located near the base of papillae. (d) Detail of a taste bud. These receptors also occur in other parts of the digestive system, such as the lining of the mouth. (Fig. 4.22). As food is chewed, it dissolves and enters the taste buds, where it sets off nerve impulses.Much like smell, sweet and bitter tastes appear to be based on a lock- andkey match between molecules and intricately shaped receptors. Saltiness and sourness, however, are triggered by a direct flow of charged atoms into the tips of taste cells (Lindemann, 2001). Taste Copyright Allyn and Bacon 2006 Taste buds Receptors for taste (primarily on the upper side of the tongue) What is the Relationship Between Perception and Sensation? Copyright Allyn and Bacon 2006 Perception brings meaning to sensation, so perception produces an interpretation of the external world, not a perfect representation of it The Gestalt Laws of Perceptual Grouping Max Wertheimer (1923) These laws suggest how our brains prefer to group stimulus elements together to form a percept Perceptual Set Readiness to detect a particular stimulus in a given context. We tend to perceive what we expect to perceive. Copyright Allyn and Bacon 2006 Making sense of the world What am I seeing? Is that something Ive seen before? Bottom-up processing: taking sensory information and then assembling and integrating it Top-down processing: using models, ideas, and expectations to interpret sensory information Gibson and Walk found that all species tested can perceive and avoid a sharp drop by the time they take up independent locomotion (About 6 months in humans) Binocular cuesMonocular cues Information processed into both eyes. Both of your eyes help strengthen your perception in depth. Depth information perceived by the use of only one eye. Although both types of cue are presented separately in this resource, in reality they all work together Retinal disparity Human eyes are spaced apart, separated by the nose. The average distance of this spacing is 7cms. This means that the brain receives two slightly different pictures of the same scene The Gestalt Laws of Perceptual Grouping Similarity Proximity Continuity Common fate Prgnanz Prgnanz We tend to order our experience in a manner that is regular, orderly, symmetric, and simple This is what makes things such as proofreading a text so difficult Reality is reduced to its simplest form Law of Pragnanz and the face on Mars People mentally process visual information that is symmetrical contains the simplest shapes possible contains the fewest number of shapes Relative Size The smaller image of two objects of the same size appears more distant Interposition Closer object blocks distant object Relative Clarity Hazy object seen as more distant Texture coarse = close fine = distant Relative Height Higher objects are farther away Relative Motion As we move, objects at different distances change their relative positions in our visual image, with those closest moving most Linear Perspective The converging of parallel lines indicates greater distance, as in looking down a road Light and Shadow Dimmer objects seem more distant. Monocular Cues Information about depth that relies on the input of one eye Relative size This photo is an example of relative size. Even though the beer bottle in the front of the picture is the same size as the one in the back of the picture, the one in front looks much bigger because its colser Relative Height In this scene the furthest objects, the trees, are also the highest. We know the boats are nearer to us than the trees because they are lower down The same effect works in real life as well as paintings The cloth of the couch is much more detailed the closer it is to the camera. The further away, the harder it is to make out the textures pattern and this Interposition or overlap We assume the tree is in front of the house because it obscures our view of it. It is superimposed on the front of the house, it overlaps it. Likewise we know the tutor is nearer to us than the blackboard because she obscures (overlaps) a portion of it Relative Motion When an observer passes through a scene it moves through the observers field of vision at different speeds Perceptual Constancy Ability to recognize the same object under different conditions, such as changes in light, distance, or location Copyright Allyn and Bacon 2006 A dog is running at you you dont perceive it as growing larger Shape Consistency: Explains why we do not see people morphing in shape as they walk past us and we see them from a different perspective. Color Consistency: Explains why a shirt will look the same shade of blue in dim light or sunlight Copyright Allyn and Bacon 2006