Monday January 30 y Bio Psych Studying Midterm 3 Lecture 14 Sensory Perception and the Visual System 1 5 Senses and What Stimuli They Are Responsive To Sight vision light energy Taste gustation chemical signals Smell olfaction chemical signals Hearing audition mechanical signals Somatosensory mechanical signals 2 3 Sensory Receptors Photoreceptors convert light energy into action potentials assoc with vision Chemoreceptors convert chemical energy into action potentials assoc with smell and taste hearing and touch Mechanoreceptors convert mechanical energy into action potentials assoc with 3 4 Factors Influencing Receptive Field Sensitivity Stimulus In tensity Quality rate of discharge change in the number of action potentials fired by the sensory re ceptor per unit time encodes presence of a sensory stimulus stimulus intensity greater intensity like a brighter light or louder noise is encoded by a greater discharge rate 1 Monday January 30 y stimulus quality red vs green light for example can be coded for by activity of dif ferent receptors or by different levels of discharge in the same receptor 5 6 Sensation vs Perception Sensation the registration of physical stimuli from the environment by sensory re ceptors Perception the subject experience of sensation Factors contributing to perception nature of the sensation context in which sensory events take place emotional state past experiences and memories 7 Fovea vs Blind Spot Distribution of Rods and Cones Fovea contains the largest density of photoreceptors area for sharpest vision driven by neurons in the midbrain move fovea around visual field to give Blind spot contains no photoreceptors photoreceptors around each blind spot fill makes up 1 of visual field saccades a bigger and more detailed picture has the most cones in missing visual info 8 Rods vs Cones Light sensitivity 2 Monday January 30 y Rods more sensitive respond to dim light Cones less sensitive respond to bright light Size shape Rods larger and cylindrical Cones smaller and tapered at end Functions Rods responsible for night vision Cones responsible for color fine detail and motion of photopigments Rods 1 Cones 3 9 Photoreceptors Photopigments Photoreceptors contain a special pigment molecule called rhodopsin When light strikes rhodopsin it activates a G protein G protein indirectly closes a Na channel Closed Na channel means less charge flowing into cell hyper polarization Hyperpolarization decreased release of glutamate by photoreceptor cell 10 Neurons involved in Neural Relay for Visual System Photoreceptors rods and cones 3 Monday January 30 y Horizontal cells link photoreceptors and send to bipolar cells Bipolar cells link photoreceptors to retinal ganglion cells Amacrine cells link bipolar cells and retinal ganglion cells Retinal ganglion cells receive info from bipolar and amacrine cells and sends info to lateral geniculate nucleus of the thalamus lateral geniculate nucleus neurons send axons to striate cortex 11 Rods vs Cones Convergence on Bipolar and Retinal Gan glion Cells More rods converge on each bipolar neuron and more rod bipolar neurons converge important for sensing dim light bipolar neurons will be activated if ANY of the rods on each rod ganglion cell get activated by light Cones have less convergence important for fine detail discrimination we want a fine map of an object Lecture 15 The Visual System and Visual Processing 1 Ventral and Dorsal Streams Ventral Stream Temporal Cortex the what path object identification Dorsal Stream Parietal Cortex the where path spatial location 2 Shape Processing in the Visual System Each retinal ganglion cell receives input from lots of nearby bipolar cells which re ceive input from lots of nearby photoreceptors rods and cones 4 Monday January 30 y each ganglion cell has a receptive field of photoreceptors that is activated when light hits the photoreceptors On center cell increases firing when light hits the center of its receptive field Each retinal ganglion cell therefore senses a single spot of light within the center of Each cell in the visual striate cortex receives input from several retinal ganglion its receptive field cells Line Detection in the Visual Cortex the temporal cortex bars in the striate cortex Input from several ganglion spot cells is summed and activates a single neuron in Ganglion input which provides info about spots is translated into lines or Different neurons in the striate cortex respond to slightly different line orientations Neurons responding to lines in different parts of the visual cortex are arranged into columns in the visual cortex Processing Shape in the Inferior Temporal Cortex Input from visual striate cortex is sent to the inferior temporal cortex via the ventral stream Input from many different line neurons in the striate cortex integrates onto single inferior temporal cortical neurons that then process these individual lines or edges into shapes Inferior temporal cortex cells therefore recognize specific shapes and are arranged into columns 5 Lateralization words are processed in the left ITC faces and places in the right ITC Generic objects are processed in the left ITC specific objects in the right ITC Monday January 30 y Processing Shape in the Inferior Temporal Cortex Striate cortex neurons with different line detection send axons that converge on sin gle temporal cortex neurons If both striate neurons are firing at a high rate simultaneously they will cause the temporal cortex neuron to fire rapidly It will fire the highest when both striate neurons are active at the same time There will therefore be a neuron Other neurons might fire highest when a or a box or a circle or a face is present and the corresponding striate neurons are firing 3 Temporal Lobe Lesions Visual form agnosia inability to recognize objects from their shape Achromatopsia inability to detect any colors Akinetopsia inability to perceive movement or moving objects 4 Processing Where Information in the Dorsal Stream of the Visual System Axons from LGN neurons extend to the striate cortex Info from the top of the visual field is sent to the bottom of the striate cortex and vice Info from left visual field is sent to right striate cortex and vice versa versa 6 Monday January 30 y Info from center of the visual field is sent into the center while info form the periphery is sent more anteriorly The fovea has a larger representation than peripheral retinal areas KEY POINT Even though axes may be