Mechanisms of Perception PDF

MECHANISMS OF PERCEPTION HEARING, TOUCH, SMELL, TASTE AND ATTENTION How you know the world 1. Name and define the three types of sensory cortex. 2. Explain the relationship between the physical and perceptual dimensions of sound. 3. Describe the components of the human ear, and...

MECHANISMS OF PERCEPTION HEARING, TOUCH, SMELL, TASTE AND ATTENTION How you know the world 1. Name and define the three types of sensory cortex. 2. Explain the relationship between the physical and perceptual dimensions of sound. 3. Describe the components of the human ear, and explain how sound is processed within its various structures. 4. Name some of the cutaneous receptors, and explain the functional significance of fast versus slow receptor adaptation. 5. Describe the two major somatosensory pathways. 6. Describe the phenomenon of change blindness Principles of Sensory System Organization  Primary sensory cortex of a system is the area of sensory cortex that receives most of its input directly from the thalamic relay nuclei of that system. Secondary sensory cortex of a system comprises the areas of the sensory cortex that receive most of their input from the primary sensory cortex of that system or from other areas of secondary sensory cortex of the same system. Association cortex is any area of cortex that receives input from more than one sensory system Features of Sensory System Organization  Hierarchical organization - is a system whose members can be assigned to specific levels or ranks in relation to one another. Psychologists sometimes divide the general process of perceiving into two general phases: Sensation is the process of detecting the presence of stimuli Perception is the higher- order process of integrating, recognizing, and interpreting complete patterns of sensations. Parallel processing— the simultaneous analysis of a signal in different ways by the multiple parallel pathways of a neural network. Two models of sensory system organization: The former model was hierarchical, functionally homogeneous, and serial; the current model, which is more consistent with the evidence, is hierarchical, functionally segregated, and parallel. not shown in the current model are the many descending pathways that are the means by which higher levels of sensory systems can influence sensory input. Auditory System  Auditory System Sounds are vibrations of air molecules that stimulate system humans hear only those molecular vibrations between about 20 and 20,000 hertz (cycles per second). Pure tones (sine wave vibrations) exist only in laboratories and sound recording studios; in real life, sound is always associated with complex patterns of vibrations. Fourier analysis is the mathematical procedure for breaking down complex waves into their component sine waves Fundamental frequency (the highest frequency of which the various component f frequencies of a sound are multiples)  The Ear 1. Waves travel from the outer ear down the auditory canal and cause the tympanic membrane (the eardrum) to vibrate. 2. Three Ossicles—the small bones of the middle ear: the malleus (the hammer), the incus (the anvil), and the stapes (the stirrup) 3. The vibrations of the stapes trigger vibrations of the membrane called the oval window, which in turn transfers the vibrations to the fluid of the snail-shaped cochlea (kokhlos means “land snail”) 4. Cochlea is a long, coiled tube with an internal structure running almost to its tip. 5. The organ of Corti is composed of several membranes; we will focus on two of them: the basilar membrane and the tectorial membrane. 6. The auditory receptors, the hair cells, are mounted in the basilar membrane, and the tectorial membrane rests on the hair cells. 7. Auditory nerve—a branch of cranial nerve VIII (the auditory- vestibular nerve). The vibrations of the cochlear fluid are ultimately dissipated by the round window, an elastic membrane in the cochlea wall. 8. Semicircular canals—the receptive organs of the vestibular system Effects of Damage to the Auditory System 1. Auditory Cortex Damage 2. Deafness in humans a) Conductive deafness is associated with damage to the ossicles. b) Nerve deafness is associated with damage to the cochlea or auditory nerve. c) Tinnitus is frequent or constant ringing in the ears. In some cases, tinnitus may be due to a phenomenon similar to phantom limb. Somatosen sory System: T ouch an d P ain 1. Exteroceptive system senses external stimuli that are applied to the skin. 2. Proprioceptive system monitors information about the position of the body that comes from receptors in the muscles, joints, and organs of balance. 3. Interoceptive system provides general information about conditions within the body (e.g., temperature and blood pressure). A. Cutaneous Receptors 2. Free nerve endings which are particularly sensitive to temperature change and pain. 3. Pacinian corpuscles acts as a receptor for pressure and vibration. 4. Merkel’s disks and ruffini endings both adapt slowly and respond to gradual skin indentation and skin stretch, respectively  Stereognosis is the identification of objects by touch. 5. Dermatome carries information from cutaneous receptors and other somatosensory receptors gather together in nerves and enter the spinal cord via the dorsal roots Somatosensory Receptors and Probable Function 2 Major Semotosensory Pathways 1. Dorsal-column medial-lemniscus system tends to carry information about touch and proprioception. 2. Anterolateral system tends to carry information about pain and temperature.  Effects of Damage to the Primary Somatosensory Cortex 1. Astereognosia—the inability to recognize objects by touch. Cases of pure astereognosia—those that occur in the absence of simple sensory deficits—are rare. 2. Asomatognosia—the failure to recognize parts of one’s own body. Asomatognosia is usually unilateral, affecting only the left side of the body, and it is usually associated with extensive damage to the right temporal and posterior parietal lobe. anosognosia—the failure of neuropsychological patients to recognize their own symptoms.  Rubber-Hand Illusion - the feeling that an extraneous object, in this case a rubber hand, is actually part of one’s own body  Perception of Pain 1. Adaptiveness of pain. One paradox of pain is that an experience that seems in every respect to be so bad is in fact extremely important for our survival. 2. Lack of clear cortical representation of pain 3. Descending pain control  Neuropathic Pain It is a severe chronic pain in the absence of a recognizable pain stimulus. develops after an injury can be triggered by an innocuous stimulus, such as a gentle touch. Emotional Pain activate a path that goes through the medulla, then to the thalamus, and then to the amygdala, hippocampus, prefrontal cortex, and anterior cingulate cortex These areas react not to the sensation itself but to its emotional aspect. Ways of Relieving Pain 1. Opioid mechanisms— systems that respond to opiate drugs and similar chemicals. 2. Endorphins - which relieve different types of pain, such as the pain from a cut versus the pain from a burn. 3. Cannabinoids and Capsaicin - Morphine and other opiates are effective pain reducers, but they have limitations 4. Placebo, a drug or other procedure with no pharmacological effects Chemical Senses Olfaction (smell) and Gustation (taste) are referred to as the chemical senses because their function is to monitor the chemical content of the environment.  Gustatory System Taste results from stimulation of the taste buds, the receptors on the tongue Taste Receptors Taste receptor cells are found on the tongue and in parts of the oral cavity; they typically occur in clusters of 50 to 100 called taste buds.  Olfactory System  Pheromones The vomeronasal organ (VNO) is a set of receptors located near, but separate from, the olfactory receptors. respond only to pheromones, chemicals released by an animal that affect the behavior of other members of the same species. Pheromones— chemicals that influence the physiology and behavior.  Synesthesia - is the experience some people have in which stimulation of one sense evokes a perception of that sense and another one also. For example, someone might perceive the letter J as green or say that each taste feels like a particular shape on the tongue.  Cocktail-party phenomenon is the fact that even when you are focusing so intently on one conversation that you are totally unaware of the content of other conversations going on around you, the mention of your name in one of the other conversations will immediately gain access to your consciousness. Change blindness is the finding that observers often fail to notice large changes to objects or scenes when the change coincides with a brief visual disruption. Visual Simultanagnosia is a difficulty in attending visually to more than one object at a time.