2 Overview of QuestionsHow can brain damage affect a person’s perception?Are there separate brain areas that determine our perception of different qualities?How has the operation of our visual system been shaped by evolution and by our day-to-day experiences?
4 Maps: Representing Spatial Layout Retinotopic map - each place on the retina corresponds to a place on the LGNDetermining retinotopic maps - record from neurons with an electrode that penetrates the LGN obliquelyLGN has 6 layersStimulating receptive fields on the retina shows the location of the corresponding neuron in the LGNLGN - Lateral Geniculate NucleusImportant to note that the receptive field for ANY neuron in the system is at the receptor cells for that modality -- for vision, that will always be the retina. Students tend to forget this and get confused later.
7 Cortex shows retinotopic map too The Map on the CortexCortex shows retinotopic map tooElectrodes recording from a cat’s visual cortex shows:Receptive fields on the retina that overlap also overlap in the cortexThis pattern is seen using an oblique penetration of the cortexIt might be helpful here to explain how the Hubel and Wiesel experiment works. Stimuli are shown on specific points on the retina to find the stimulus and the receptive field that stimulates a neuron in the cortex that is being monitored by an electrode. This is also a good place to discuss ethics in the use of the animals for research, if the instructor desires to do so.
9 The Map on the Cortex - continued Cortical magnification factorFovea has more cortical space than expectedFovea accounts for .01% of retinaSignals from fovea account for 8% to 10% of the visual cortexThis provides extra processing for high-acuity tasksHow do we know this stuff?
10 Brain Imaging Techniques Positron emission tomography (PET)Person is injected with a harmless radioactive tracerTracer moves through bloodstreamMonitoring the radioactivity measures blood flowChanges in blood flow show changes in brain activityThe instructor can connect this section on brain imaging techniques by explaining to the students that these methods have been used to provide evidence for the magnification factor for the fovea found in the visual cortex.
12 Brain Imaging Techniques - continued Functional magnetic resonance imaging (fMRI) measures blood flow by:Hemoglobin carries oxygen and contains a ferrous molecule that is magneticBrain activity takes up oxygen, which makes the hemoglobin more magneticfMRI determines activity of areas of the brain by detecting changes in magnetic response of hemoglobinSubtraction technique is used like in PET
13 Purple and teal areas show the extent of stimuli that were presented while a person was in an fMRI scanner. (b) Purple and teal indicates areas of the brain activated by the stimulation in (a).
14 Organization in Columns LGN receives signals for right and left eyesLayers 2, 3, and 5 receive input from the ipsilateral eyeLayers 1, 4, and 6 receive input from the contralateral eyeElectrodes inserted perpendicular to the surface show that receptive fields along the track are in the same location in the retinaNote: make sure to remind students that there is an LGN in both hemispheres.You can also tell them they can use the prefix “contra” as a memory aid for the term contralateral. Finally, this is a good place to point out that the separation of the input from the right and left eye is the first place that brain compares the slightly different images from each eye which begin the process of 3-D vision.
16 Organization in Columns - continued Visual cortex shows:Location columnsReceptive fields at the same location on the retina are within a columnOrientation columnsNeurons within columns fire maximally to the same orientation of stimuliAdjacent columns change preference in an orderly fashion1 millimeter across the cortex represents entire range of orientation
17 Figure 4.9 When an electrode penetrates the cortex perpendicularly, the receptive fields of the neurons encountered along this track overlap. The receptive field recorded at each numbered position along the electrode track is indicated by a correspondingly numbered square.
18 All of the cortical neurons encountered along track A respond best to horizontal bars (indicated by the red lines cutting across the electrode track.) All of the neurons along track B respond best to bars oriented at 45 degrees.
19 Organization in Columns - continued Visual cortex shows (cont.)Ocular dominance columnsNeurons in the cortex respond preferentially to one eyeNeurons with the same preference are organized into columnsThe columns alternate in a left-right pattern every .25 to .50 mm across the cortex
20 This slide can be used to talk about the entire process using this image as an example for how incoming stimulation is organized beginning with the neurons in the retina, through the LGN and into the cortex. The text has material on this that can be added to the lecture.Figure 4.11 (a) How a peppermint stick creates an image on the retina and a pattern of activation on the cortex. (b) How a long peppermint stick would activate a number of different orientation columns in the cortex.
21 Lesioning or Ablation Experiments An animal is trained to indicate perceptual capacitiesA specific part of the brain is removed or destroyedThe animal is retrained to determine which perceptual abilities remainThe results reveal which portions of the brain are responsible for specific behaviors
22 What and Where Pathways Ungerleider and Mishkin (1983)Object discrimination problemMonkey is shown an objectThen presented with two choice taskReward given for detecting the targetLandmark discrimination problemMonkey is trained to pick the food well next to a cylinder
23 What and Where Pathways - continued Ungerleider and Mishkin (cont.)Using ablation, part of the parietal lobe was removed from half the monkeys and part of the temporal lobe was removed from the other halfRetesting the monkeys showed that:Removal of temporal lobe tissue resulted in problems with the landmark discrimination task - What pathway(I see it, but don’t know where it is)Removal of parietal lobe tissue resulted in problems with the object discrimination task - Where pathway(I know where it is, but I don’t know what it is)
24 The monkey cortex, showing the what, or ventral pathway from the occipital lobe to the temporal lobe, and the where, or dorsal pathway from the occipital lobe to the parietal lobe.
25 What and Where Pathways - continued What pathway also called doral pathwayWhere pathway also called ventral pathwayBoth pathways originate in retinaVentral pathway begins in small or medium ganglion cellsCalled P-cellsAxons synapse in layers 3, 4, 5, & 6 of LGNCalled parvocellular layers
26 What and Where Pathways - continued Dorsal pathway begins in large ganglion cellsCalled M-cellsAxons synapse in layers 1 & 2 of LGNCalled magnocellular layersAblation research with monkeys shows:Parvo channels send color, texture, shape and depth informationMagno channels send motion information
27 Make sure to note here that the even though the pathways have different functions, they have interconnections, and there is a feedback loop for information within both systems.The dorsal and ventral streams in the cortex originate with the magno and parvo ganglion cells and the magno and parvo layers of the LGN. The red arrow represents connections between the streams. The dashed blue arrows represent feedback - signals that flow “backward.”
29 What and Where Pathways - continued Where pathway may actually be “How” pathwayDorsal stream shows function for both location and for actionEvidence from neuropsychologySingle dissociations: two functions involve different mechanismsDouble dissociations: two functions involve different mechanisms and operate independentlyNote the neuropsychology involves the study of the behavioral effects of brain damage.
30 Table 4.2 Double dissociations in TV sets and people.
31 What and How Pathways - Neuropsycholgical Evidence Behavior of patient D.F.Damage to ventral pathway due to gas leakNot able to match orientation of card with slotBut was able to match orientation if she was placing card in a slotOther patients show opposite effectsEvidence shows double dissociation between ventral and dorsal pathwaysThis shows explicitly the double dissociation between judging orientation and the coordination of vision and action. It also shows that the how pathway (where pathway) could also be called the action pathway.
33 What and How Pathways - Further Evidence Rod and frame illusionObservers perform two tasks: matching and graspingMatching task involves ventral (what) pathwayGrasping task involves dorsal (how) pathwayResults show that the frame orientation affects the matching task but not the grasping task
34 Figure 4. 17 (a) Rod and frame illusion Figure 4.17 (a) Rod and frame illusion. Both small lines are oriented vertically. (b) Matching task and results. (c) Grasping task and results. See text for details.
35 Modularity: Structures for Faces, Places, and Bodies Module - a brain structure that processes information about specific stimuliInferotemporal (IT) cortex in monkeysOne part responds best to faces while another responds best to headsResults have led to proposal that IT cortex is a form perception moduleTemporal lobe damage in humans results in prosopagnosia
36 Figure (a) Monkey brain showing location of the inferotemporal cortex (IT) in the lower part of the temporal lobe. (b) Human brain showing location of the fusiform face area (FFA) in the fusiform gyrus, which is located under the temporal lobe.
38 Modularity: Structures for Faces, Places, and Bodies - continued Evidence from humans using fMRI and the subtraction technique show:Fusiform face area (FFA) responds best to faces as well as when context implies a faceParahippocampal place area (PPA) responds best to spatial layoutExtrastriate body area (EBA) responds best to pictures of full bodies and body partsNote the the EBA does NOT respond to faces.
39 Figure 4. 21 fMRI response of the human fusiform face area Figure 4.21 fMRI response of the human fusiform face area. Activation occurs when a face is present (E) or is implied (D) but is lower when other stimuli are presented (A,B,C,F). (Reprinted with permission from Cox, D., Meyers, E., Sinha, P. (2004). Contextually evoked object-specific responses in human visual cortex, Science, 304,
40 Evolution and Plasticity: Neural Specialization Evolution is partially responsible for shaping sensory responses:Newborn monkeys respond to direction of movement and depth of objectsBabies prefer looking at pictures of assembled parts of facesThus “hardwiring” of neurons plays a part in sensory systems
41 Evolution and Plasticity: Neural Specialization - continued Plasticity of neurons also shapes sensory responsesExperience-dependent plasticity in animalsMonkeys trained to recognize specific view of unfamiliar objectOther views of object showed decline in recognition as object rotated from trained viewNeurons in the IT cortex showed maximal response to the trained orientationNote: You can also refer to experiment with kittens raised in vertical only environment that are mentioned in Chapter 3.You can also refer to the stimulus-perception relationship and stimulus physiological relationship demonstrated in this experiment.
42 Figure 4. 23 (a) Stimuli like those used by Logothetis & Pauls (1995) Figure 4.23 (a) Stimuli like those used by Logothetis & Pauls (1995). (b) Monkey’s ability to recognize the training shape and rotated views of the shape that were not seen during training. (c) Response of neurons in the IT cortex of the trained monkey to the training shape and the rotated shape.
43 Evolution and Plasticity: Neural Specialization - continued Experience-dependent plasticity in humansBrain imaging experiments show areas that respond best to letters and wordsfMRI experiments show that training results in areas of the FFA responding best to:Greeble stimuliCars and birds for experts in these areas
44 Figure 4. 24 (a) Greeble stimuli used by Gauthier Figure 4.24 (a) Greeble stimuli used by Gauthier. Participants were trained to name each different Greeble. (b) Brain responses to Greebles and faces before and after Greeble training. (a: From Figure 1a, p. 569, from Gauthier, I., Tarr, M. J., Anderson, A. W., Skudlarski, P. L., & Gore, J. C. (1999). Activation of the middle fusiform “face area” increases with experience in recognizing novel objects. Nature Neuroscience, 2, )
45 Figure 4.25 Ways that the brain is organized. This slide can act as a summary of the information presented so far that pertains to how the visual system is organized and how their are specific response to specific stimuli. This then leads to the material in the next section on how stimuli are coded specifically by neural firing.Figure Ways that the brain is organized.
46 Sensory Code: Representation of Environment Sensory code - representation of perceived objects through neural firingSpecificity coding - specific neurons responding to specific stimuliLeads to the “grandmother cell” hypothesisRecent research shows cells in the hippocampus that respond to concepts such as Halle Berry
47 Figure 4.29 (a) Location of the hippocampus and some of the other structures that were studied by Quiroga and coworkers (2005)
48 Sensory Code: Representation of Environment - continued Problems with specificity coding:Too many different stimuli to assign specific neuronsMost neurons respond to a number of different stimuliDistributed coding - pattern of firing across many neurons codes specific objectsLarge number of stimuli can be coded by a few neurons
49 Sensory Code: Representation of Environment - continued Coding can be distributed across many brain areasMonkeys’ IT cortex shows overlap of activation caused by different stimulifMRI experiments with humans show the same type of effectThus, although there is specific response within modules, there is also activation across modules for specific stimuli
50 Figure 4.26 How faces could be coded according to (a) specificity coding and (b) distributed coding. The height of the bars indicates the response of neurons 1, 2, and 3 to each stimulus face. See text for explanation.