Power Point Presentation for Biopsychology 8 th Edition

Power. Point Presentation for Biopsychology, 8 th Edition by John P. J. Pinel Prepared by Jeffrey W. Grimm Western Washington University Copyright © 2011 Pearson Education, Inc. All rights reserved. This multimedia product and its contents are protected under copyright law. The following are prohibited by law: • any public performance or display, including transmission of any image over a network; • preparation of any derivative work, including the extraction, in whole or in part, of any images; • any rental, lease, or lending of the program.

Chapter 6: The Visual System How We See Copyright © 2011 Pearson Education, Inc.

What Do We See? Somehow a distorted and upside-down 2 -D retinal image is transformed into the 3 -D world we perceive l Two types of research needed to study vision l l l Research probing the components of the visual system Research assessing what we see Copyright © 2011 Pearson Education, Inc. All rights reserved.

Light Enters the Eye and Reaches the Retina l l No species can see in the dark, but some are capable of seeing when there is little light Light can be thought of as l l l Particles of energy (photons) Waves of electromagnetic radiation Humans see light between 380 -760 nanometers Wavelength – perception of color Intensity – perception of brightness Copyright © 2011 Pearson Education, Inc. All rights reserved.

FIGURE 6. 2 The electromagnetic spectrum and the colors associated with the wavelengths that

The Pupil and the Lens l l l Light enters the eye through the pupil, whose size changes in response to changes in illumination Sensitivity – the ability to see when light is dim Acuity – the ability to see details Copyright © 2011 Pearson Education, Inc. All rights reserved.

The Pupil and the Lens Continued l l l Lens – focuses light on the retina Ciliary muscles alter the shape of the lens as needed Accommodation – the process of adjusting the lens to bring images into focus Copyright © 2011 Pearson Education, Inc. All rights reserved.

FIGURE 6. 3 The human eye. Copyright © 2011 Pearson Education, Inc. All rights

Eye Position and Binocular Disparity l l l Convergence – eyes must turn slightly inward when objects are close Binocular disparity – difference between the images on the two retinas Both are greater when objects are close – provides brain with a 3 -D image and distance information Copyright © 2011 Pearson Education, Inc. All rights reserved.

The Retina and Translation of Light into Neural Signals l The retina is in a sense “inside-out” l l l Light passes through several cell layers before reaching its receptors Vertical pathway – receptors > bipolar cells > retinal ganglion cells Lateral communication l Horizontal cells l Amacrine cells Copyright © 2011 Pearson Education, Inc. All rights reserved.

FIGURE 6. 5 The cellular structure of the mammalian retina. Copyright © 2011 Pearson

The Retina and Translation of Light into Neural Signals Continued l Blind spot: no receptors where information exits the eye l l The visual system uses information from cells around the blind spot for “completion, ” filling in the blind spot Fovea: high acuity area at center of retina l Thinning of the ganglion cell layer reduces distortion due to cells between the pupil and the retina Copyright © 2011 Pearson Education, Inc. All rights reserved.

FIGURE 6. 6 A section of the retina. Copyright © 2011 Pearson Education, Inc.

Cone and Rod Vision l Duplexity theory of vision – cones and rod mediate different kinds of vision l l Cones – photopic (daytime) vision l High-acuity color information in good lighting Rods – scotopic (nighttime) vision l High-sensitivity, allowing for low-acuity vision in dim light, but lacks detail and color information More convergence in rod system, increasing sensitivity while decreasing acuity Only cones are found at the fovea Copyright © 2011 Pearson Education, Inc. All rights reserved.

FIGURE 6. 8 A schematic representation of the convergence of cones and rods on

FIGURE 6. 9 The distribution of cones and rods over the human retina. (Adapted

Spectral Sensitivity Lights of the same intensity but different wavelengths may not all look as bright l A spectral sensitivity curve shows the relationship between wavelength and brightness l There are different spectral sensitivity curves for photopic (cone) vision and scotopic (rod) vision l Copyright © 2011 Pearson Education, Inc. All rights reserved.

FIGURE 6. 10 Human photopic (cone) and scotopic (rod) spectral sensitivity curves. Copyright ©

Eye Movement l l We continually scan the world with small and quick eye movements – saccades These bits of information are then integrated Stabilize retinal image – see nothing Visual system responds to change Copyright © 2011 Pearson Education, Inc. All rights reserved.

Visual Transduction: The Conversion of Light to Neural Signals l l Transduction – conversion of one form of energy to another Visual transduction – conversion of light to neural signals by visual receptors Pigments absorb light Absorption spectrum describes spectral sensitivity Copyright © 2011 Pearson Education, Inc. All rights reserved.

FIGURE 6. 11 The adsorption spectrum of rhodopsin compared with the human scotopic spectral

Visual Transduction: The Conversion of Light to Neural Signals Continued l l l Rhodopsin is the pigment found in rods A G protein-linked receptor that responds to light rather than to neurotransmitters In the dark l l Na+ channels remain partially open (partial depolarization), releasing glutamate When light strikes l l Na+ channels close Rods hyperpolarize, inhibiting glutamate release Copyright © 2011 Pearson Education, Inc. All rights reserved.

FIGURE 6. 12 The inhibitory response of rods to light. Copyright © 2011 Pearson

From Retina to Primary Visual Cortex l l l The retinal-geniculate-striate pathways are about 90% of axons of retinal ganglion cells The left hemiretina of each eye (right visual field) connects to the right lateral geniculate nucleus (LGN); the right hemiretina (left visual field) connects to the left LGN Most LGN neurons that project to primary visual cortex (V 1, striate cortex) terminate in the lower part of cortical layer IV Copyright © 2011 Pearson Education, Inc. All rights reserved.

FIGURE 6. 13 The retina-geniculatestriate system: the neural projections from the retinas through the lateral geniculate nuclei to the left and right primary visual cortex (striate cortex). The colors indicate the flow of information from various parts of the receptive fields of each eye to various parts of the visual system. (Adapted from Netter, 1962. ) Copyright © 2011 Pearson Education, Inc. All rights reserved.

Retinotopic Organization l l l Information received at adjacent portions of the retina remains adjacent in the striate cortex (retinotopic) More cortex is devoted to areas of high acuity – like the disproportionate representation of sensitive body parts in somatosensory cortex About 25% of primary visual cortex is dedicated to input from the fovea Copyright © 2011 Pearson Education, Inc. All rights reserved.

The M and P Channels l Magnocellular layers (M layers) l l Big cell bodies, bottom two layers of LGN Particularly responsive to movement Input primarily from rods Parvocellular layers (P layers) l l l Small cell bodies, top four layers of LGN Color, detail, and still or slow objects Input primarily from cones Copyright © 2011 Pearson Education, Inc. All rights reserved.

The M and P Channels Continued l l Project to slightly different areas in lower layer IV in striate cortex, M neurons just above the P neurons Project to different parts of visual cortex beyond V 1 Copyright © 2011 Pearson Education, Inc. All rights reserved.

Seeing Edges l Contrast Enhancement l l l Mach bands: nonexistent stripes the visual system creates for contrast enhancement Makes edges easier to see A consequence of lateral inhibition Copyright © 2011 Pearson Education, Inc. All rights reserved.

FIGURE 6. 14 The illusory bands visible in this figure are often called Mach bands, although Mach used a different figure to generate them in his studies (see Eagleman, 2001). Copyright © 2011 Pearson Education, Inc. All rights reserved.

FIGURE 6. 15 How lateral inhibition produces contrast enhancement. (Adapted from Ratliff, 1972. )

Receptive Fields of Visual Neurons l l The area of the visual field within which it is possible for a visual stimulus to influence the firing of a given neuron Hubel and Wiesel looked at receptive fields in cat retinal ganglion, LGN, and lower layer IV of striate cortex Copyright © 2011 Pearson Education, Inc. All rights reserved.

Receptive Fields: Neurons of the Retina-Geniculate-Striate System l Similarities seen at all three levels: l l Receptive fields of foveal areas are smaller than those in the periphery Neurons’ receptive fields are circular in shape Neurons are monocular Many neurons at each level had receptive fields with excitatory and inhibitory area Copyright © 2011 Pearson Education, Inc. All rights reserved.

Receptive Fields: Neurons of the Retina-Geniculate-Striate System Continued l l Many cells have receptive fields with a center -surround organization: excitatory and inhibitory regions separated by a circular boundary Some cells are “on-center” and some are “off -center” Copyright © 2011 Pearson Education, Inc. All rights reserved.

FIGURE 6. 17 The responses of an oncenter cell to contrast. Copyright © 2011

Receptive Fields: Simple and Complex Cortical Cells l l In lower layer IV of the striate cortex, neurons with circular receptive fields (as in retinal ganglion cells and LGN) are rare Most neurons in V 1 are either l l Simple – receptive fields are rectangular with “on” and “off” regions, or Complex – also rectangular, larger receptive fields, respond best to a particular stimulus anywhere in its receptive field Copyright © 2011 Pearson Education, Inc. All rights reserved.

Receptive Fields: Simple and Complex Cortical Cells Continued SIMPLE l Rectangular l “On” and “off” regions, like cells in layer IV l Orientation and location sensitive l All are monocular COMPLEX l Rectangular l Larger receptive fields l Do not have static “on” and “off” regions l Not location sensitive l Motion sensitive l Many are binocular Copyright © 2011 Pearson Education, Inc. All rights reserved.

Columnar Organization of Primary Visual Cortex l l Cells with simpler receptive fields send information on to cells with more complex receptive fields Functional vertical columns exist such that all cells in a column have the same receptive field and ocular dominance Ocular dominance columns – as you move horizontally, the dominance of the columns changes Retinotopic organization is maintained Copyright © 2011 Pearson Education, Inc. All rights reserved.

FIGURE 6. 19 The organization of the primary visual cortex: the receptivefield properties of cells encountered along typical vertical and horizontal electrode tracks in the primary visual cortex. Copyright © 2011 Pearson Education, Inc. All rights reserved.

Plasticity of Receptive Fields of Neurons in the Visual Cortex l Plasticity appears to be a fundamental property of visual cortex function l e. g. receptive field properties depend on the scene in which the stimuli to its field are embedded Copyright © 2011 Pearson Education, Inc. All rights reserved.

Seeing Color: Component and Opponent Processing l Component theory (trichromatic theory) l l Proposed by Young, refined by Helmholtz Three types of receptors, each with a different spectral sensitivity Copyright © 2011 Pearson Education, Inc. All rights reserved.

Seeing Color: Component and Opponent Processing Continued l l Opponent-process Theory proposed by Hering: Two different classes of cells encoding color, and another class encoding brightness Each encodes two complementary color perceptions Accounts for color afterimages and colors that cannot appear together (reddish green or bluish yellow) Copyright © 2011 Pearson Education, Inc. All rights reserved.

LO 3. 3 How eyes see and see colors Menu

Seeing Color: Component and Opponent Processing Continued l Both theories are correct: coding of color by cones seems to operate on a purely component basis, opponent processing of color is seen at all subsequent levels Copyright © 2011 Pearson Education, Inc. All rights reserved.

FIGURE 6. 21 The absorption spectra of the three classes of cones. Copyright ©

Color Constancy and the Retinex Theory l l l Color constancy – color perception is not altered by varying reflected wavelengths Retinex theory (Land)– color is determined by the proportion of light of different wavelengths that a surface reflects Relative wavelengths are constant, so perception is constant l l Dual-opponent color cells are sensitive to color contrast Found in cortical “blobs” Copyright © 2011 Pearson Education, Inc. All rights reserved.

FIGURE 6. 22 The method of Land’s (1977) color-vision experiments. Subjects viewed Mondrians that were illuminated by various proportions of three different wavelengths: a short wavelength, a middle wavelength, and a long wavelength. Copyright © 2011 Pearson Education, Inc. All rights reserved.

Cortical Mechanisms of Vision and Conscious Awareness l Flow of visual information: l l l Thalamic relay neurons, to 1˚ visual cortex (striate), to 2˚ visual cortex (prestriate), to Visual association cortex As visual information flows through hierarchy, receptive fields l l become larger respond to more complex and specific stimuli Copyright © 2011 Pearson Education, Inc. All rights reserved.

FIGURE 6. 24 The visual areas of the human cerebral cortex. Copyright © 2011

Damage to Primary Visual Cortex l Scotomas l l l Areas of blindness in contralateral visual field due to damage to primary visual cortex Detected by perimetry test Completion l Patients may be unaware of scotoma – missing details supplied by “completion” Copyright © 2011 Pearson Education, Inc. All rights reserved.

FIGURE 6. 26 The completion of a migraineinduced scotoma as described by Karl Lashley

Damage to Primary Visual Cortex Continued l Blindsight l l Response to visual stimuli outside conscious awareness of “seeing” Possible explanations of blindsight l l Islands of functional cells within scotoma Direct connections between subcortical structures and secondary visual cortex, not available to conscious awareness Copyright © 2011 Pearson Education, Inc. All rights reserved.

l l Functional Areas of Secondary and Association Visual Cortex Neurons in each area respond to different visual cues, such as color, movement, or shape Lesions of each area results in specific deficits Anatomically distinct (about 12 functionally distinct areas identified so far) Retinotopically organized Copyright © 2011 Pearson Education, Inc. All rights reserved.

FIGURE 6. 27 Some of the visual areas that have been identified in the

Dorsal and Ventral Streams l Dorsal stream: pathway from primary visual cortex to dorsal prestriate cortex to posterior parietal cortex l l l The “where” pathway (location and movement), or Pathway for control of behavior (e. g. reaching) Ventral stream: pathway from primary visual cortex to ventral prestriate cortex to inferotemporal cortex l l The “what” pathway (color and shape), or Pathway for conscious perception of objects Copyright © 2011 Pearson Education, Inc. All rights reserved.

FIGURE 6. 29 The “where” versus “what” and the “control of behavior” versus “conscious

Prosopagnosia l l l Inability to distinguish among faces Most prosopagnosic’s recognition deficits are not limited to faces Prosopagnosia is associated with damage to the ventral stream between the occipital and temporal lobes Prosopagnosics may be able to recognize faces in the absence of conscious awareness Prosopagnosics have different skin conductance responses to familiar faces compared to unfamiliar faces, even though they reported not recognizing any of the faces Copyright © 2011 Pearson Education, Inc. All rights reserved.

Akinetopsia l l l Deficiency in the ability to see movement progress in a normal smooth fashion Can be induced by a high dose of certain antidepressants Associated with damage to the middle temporal (MT) area of the cortex Copyright © 2011 Pearson Education, Inc. All rights reserved.