multiplechoicequestions.docx

chapter Sensation and Perception ------------------------ \ OUTLINE ### Senses, Sensation, and Perception ### Sensation: Early Perceptual Processing ##### Shared Processing From Acquisition to Anatomy ##### Receptors Share Responses to Stimuli Primary somatosensory cortex ### Audition #####...

chapter Sensation and Perception ------------------------ \ OUTLINE ### Senses, Sensation, and Perception ### Sensation: Early Perceptual Processing ##### Shared Processing From Acquisition to Anatomy ##### Receptors Share Responses to Stimuli Primary somatosensory cortex ### Audition ##### Mechanisms of Cortical Plasticity \ TAKE-HOME MESSAGES - Corpuscles located in the skin respond to somatosen- sory touch information. - Nociceptors (free nerve endings) respond to pain and temperature information. - Nerve cells at the junctions of muscles and tendons provide proprioceptive information. - Primary somatosensory cortex (S1) contains a homun- culus of the body, wherein the more sensitive regions encompass relatively larger areas of cortex. - Somatosensory representations exhibit plasticity, showing variation in extent and organization as a function of individual experience. ### Vision ##### Neural Pathways of Vision Optic nerve fibers Ganglion cells Receptor cells TAKE-HOME MESSAGES - Light activates the photoreceptors, the rods and cones, on the retina. - The optic nerve is formed from the axons of the ganglion cells, some of which decussate at the optic chiasm. - Axons in the optic nerve synapse on the LGN, and from the LGN become the optic radiations that are sent to V1. - Ten percent of the fibers from the retina innervate non- LGN subcortical structures, including the pulvinar and superior colliculus. TAKE-HOME MESSAGES - Visual neurons respond only to a stimulus that is presented in a specific region of space. This property is known as the receptive field of the cell. - Visual cells form an orderly mapping between spatial location and the neural representation of that dimension. In vision, these topographic representations are referred to as retinotopic maps. ##### Cortical Visual Areas PO 7a V4 TEO B A C primary visual cortex 0 a. As the recording electrode is moved along the cortex, the preferred orientation of the cells continuously varies. The preferred orientation is plotted as a function of the location of the electrode. b. The orientation columns are crossed with ocular dominance columns to form a cortical module. Within a module, the cells have similar receptive fields (location sensitivity), but they vary based on input source (left or right eye) and sensitivity to orientation, color, and size. For example, the so-called blobs contain cells that are sensitive to color and finer details in the visual input. This organization is repeated for each module. 100 75 50 25 0 a. A rectangle was moved through the receptive field of this cell in various directions. The red traces beside the stimulus cartoons indicate the responses of the cell to these stimuli. In the polar graph, the firing rates are plotted; the angular direction of each point indicates the stimulus direction, and the distance from the center indicates the firing rate as a percentage of the maximum firing rate. The polygon formed when the points are connected indicates that the cell was maximally responsive to stimuli moved down and to the left; the cell re- sponded minimally when the stimulus moved in the opposite direction. **(b)** This graph shows speed tuning for a cell in MT. In all conditions, the motion was in the optimal direction. This cell responded most vigorously when the stimulus moved at 64°/s. a. as flattened maps, are shown in Figure 5.30. In the flat  **b** a. The circular displays at the bottom represent the display on which a stimulus was projected, with the person instructed to fixate at the center of the crosshair. Across the scanning run, the position of the stimulus spans visual space. Left side shows color coding of activation patterns on flat map of visual cortex when the angular position of a stimulus was varied. For example, areas responding when the stimulus was presented below fixation are coded as red. Multiple retinotopic maps are evident in dorsal and ventral regions. Right side shows color coding of activation patterns when the eccentricity of the stimulus was varied (e.g., dark purple indicates activation areas when stimulus was at center of fixation). b. Position of visual areas shown in (a) on an inflated brain. The size and location can only be approxi- mated in a lateral view of the 3-d image. TAKE-HOME MESSAGES - The visual cortex is made up of many distinct regions. These regions are defined by their distinct, retinotopic maps. The visual areas have functional differences that reflect the types of computations performed by cells within the areas. For instance, cells in area V4 are sensitive to color information, and cells in V5 are sensitive to motion information. - Humans also have visual areas that do not correspond to any region in our close primate relatives. ### From Sensation to Perception ##### Where Are Percepts Formed?  --2 0 2 4 6 8 10 12 14 16 18 --2 0 2 4 6 8 10 12 14 16 18 a. Flickering pinwheel stimulus for studying limits of temporal resolution. The left and right stimuli alternated at different rates or contrast. **(b)** BOLD response to the flickering stimuli in three visual areas, V1, hV4, and VO. The activation profile in VO matches the participants' perceptual experience since the color changes in the stimulus were invisible at the high 30 Hz rate or when the contrast was below threshold. In contrast, the activation profile in V1 and hV4 is correlated with the actual stimulus when the contrast was above threshold. a b 15 s a. Participants viewed an annulus in which the lines were either oriented in only one direction (target) or both directions (mask). b. In some trials, the target was presented for only 17 ms and was preceded by the mask. On these trials, the target was not visible to the participant. A pattern classifier was used to predict from the fMRI data if the target was oriented to the left or right. When the stimulus was visible, the classifier was very accurate when using data from V1, V2, or V3. When the stimulus was invisible due to the mask, the clas- sifier only achieved above chance performance for the data from V1.  a. Discrimination task 0.8 0.6 0.4 0.2 b. Motion strength (% coh) ##### Individual Differences in Perception TAKE-HOME MESSAGES - Our percepts are more closely related to activity in higher visual areas than to activity in primary visual cortex. - Anatomical differences among people in the size of V1 affect the extent of visual illusion. ### Deficits in Visual Perception ##### Deficits in Color Perception: Achromatopsia **a** 100 0 a. MRI scans showing a small lesion encompassing V4 in the right hemisphere. b. Color perception thresholds in each visual quadrant. The patient was severely impaired on the hue- matching task when the test color was presented to the upper left visual field. The *y*-axis indicates the color required to detect a difference between a patch shown in each visual quadrant (UL = upper left, ##### Deficits in Motion Perception: Akinetopsia **FIGURE 5.40 Two portraits.** **a** 100 90 TMS of b. motor cortex ##### Perception Without a Visual Cortex c. Lesion of colliculus d. Lesion of visual cortex TAKE-HOME MESSAGES - Superior colliculus lesions impair the ability of an animal to orient toward the position of a stimulus (which is important for spatial orientation); visual cortex lesions impair visual acuity (which is important for object identification). - Achromatopsia, the inability to perceive color, results from lesions to areas in and around human V4. - These regions do not just represent color, however; they - Akinetopsia, the inability to process motion, results from lesions to area V5 (human MT). - As with many neurological conditions, the deficit can be quite subtle for unilateral lesions. ### Multimodal Perception: I See What You're Sayin' ##### Multimodal Processing in the Brain 0 --10 --20 --30 \ TAKE-HOME MESSAGES - Some areas of the brain, such as the superior colliculus and superior temporal sulci, process information - When multisensory information is presented coincidently in time and space, the multisensory neural response is enhanced. The reverse is also true; when multisensory ##### Errors in Multimodal Processing: Synesthesia a c b Audiotactile Visuotactile \ TAKE-HOME MESSAGES - People with synesthesia experience a mixing of the senses, for example, colored hearing, colored graphemes, or colored taste. - Synthesia is associated with both abnormal activation patterns in functional imaging studies and abnormal patterns of connectivity in structural imaging studies. ### Perceptual Reorganization 0.25 0.50 0.00 **c** Day 1 Day 3 Day 5 Day 6 a. fMRI activation during tactile exploration. By Day 5, the blindfolded group showed greater activa- tion than the controls in the occipital cortex. This effect disappeared after the blindfold was removed. b. Performance on tactile acuity after one or five days of practice. Lower values correspond to greater sensitivity. (Green: blindfolded participants; Red: Controls.) **(c)** Difference in occipital activation between blindfolded and control participants across days. TAKE-HOME MESSAGES - Following sensory deprivation, the function of sensory regions of the cortex may become reorganized, or exhibit what is called plasticity. - For instance, in blind individuals, areas of the brain that are usually involved in visual function may become part of the somatosensory cortex. - Plasticity can also be observed in healthy individuals if they are deprived of information from one sensory modality for even relatively short periods of time.