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October, 2006
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Visual Cortex: Area of the occipital lobe concerned with vision.

Finding Your Blind Spot and Perceptual Filling-in

JoVE 10195

Source: Laboratory of Jonathan Flombaum—Johns Hopkins University

In the back of everyone's eye is a small piece of neural tissue called the retina. The retina has photosensitive cells that respond to stimulation by light. The responses of these cells are sent into the brain through the optic nerve, a bundle of neural fibers. In each retina there is a place somewhere in the periphery where the outputs from retinal cells collect and the bundled optic nerve exits to the brain. At that location, there is no photosensitivity-whatever light reflects from the world and lands in that position does not produce a signal in the brain. As a result, humans have a blind spot, a place in the visual field for which they don't process incoming stimuli. However, people are not aware that they have blind spots; there is not an empty hole in the visual images in front of the eyes. So what do people see in their blind spots? The brain actually fills-in missing input based on the surroundings. This video demonstrates how to find a person's blind spot, and how to investigate the mechanisms of perceptual filling-in.

 Sensation and Perception

Visual Attention: fMRI Investigation of Object-based Attentional Control

JoVE 10272

Source: Laboratories of Jonas T. Kaplan and Sarah I. Gimbel— University of Southern California

The human visual system is incredibly sophisticated and capable of processing large amounts of information very quickly. However, the brain's capacity to process information is not an unlimited resource. Attention, the ability to selectively process information that is relevant to current goals and to ignore information that is not, is therefore an essential part of visual perception. Some aspects of attention are automatic, while others are subject to voluntary, conscious control. In this experiment we explore the mechanisms of voluntary, or "top-down" attentional control on visual processing. This experiment leverages the orderly organization of visual cortex to examine how top-down attention can selectively modulate the processing of visual stimuli. Certain regions of the visual cortex appear to be specialized for processing specific visual items. Specifically, work by Kanwisher et al.1 has identified an area in the fusiform gyrus of the inferior temporal lobe that is significantly more active when subjects view faces compared to when they observe other common objects. This area has come to be known as the Fusiform Face Area (FFA). Another brain region, known as the Para


Color Afterimages

JoVE 10194

Source: Laboratory of Jonathan Flombaum—Johns Hopkins University

Human color vision is impressive. People with normal color vision can tell apart millions of individual hues. Most amazingly, this ability is achieved with fairly simple hardware.

Part of the power of human color vision comes from a clever bit of engineering in the human brain. There, color perception relies on what is known as an 'opponent system.' This means that the presence of one kind of stimulus is treated as evidence for the absence of another, and vice versa; absence of one kind of stimulus is taken as evidence for the presence of the other. In particular, in the human brain there are cells that fire both when they receive signals to suggest that blue light is present, or when they do not receive signals suggesting yellow light. Similarly, there are cells that fire in the presence of yellow or the absence of blue. Blue and yellow are thus treated as opponent values in one dimension, and can be thought of as negative versus positive values on one axis of a Cartesian plane. If a stimulus is characterized as having a negative value on that axis, it can't also have a positive value. So, if it is characterized as yellow, it can't also be characterized as blue. Similarly, green and red (or really, magenta), o

 Sensation and Perception

Decoding Auditory Imagery with Multivoxel Pattern Analysis

JoVE 10267

Source: Laboratories of Jonas T. Kaplan and Sarah I. Gimbel—University of Southern California

Imagine the sound of a bell ringing. What is happening in the brain when we conjure up a sound like this in the "mind's ear?" There is growing evidence that the brain uses the same mechanisms for imagination that it uses for perception.1 For example, when imagining visual images, the visual cortex becomes activated, and when imagining sounds, the auditory cortex is engaged. However, to what extent are these activations of sensory cortices specific to the content of our imaginations? One technique that can help to answer this question is multivoxel pattern analysis (MPVA), in which functional brain images are analyzed using machine-learning techniques.2-3 In an MPVA experiment, we train a machine-learning algorithm to distinguish among the various patterns of activity evoked by different stimuli. For example, we might ask if imagining the sound of a bell produces different patterns of activity in auditory cortex compared with imagining the sound of a chainsaw, or the sound of a violin. If our classifier learns to tell apart the brain activity patterns produced by these three stimuli, then we can conclude that the auditory cortex is activated in a distinct


Object Substitution Masking

JoVE 10279

Source: Laboratory of Jonathan Flombaum—Johns Hopkins University

Visual masking is a term used by perceptual scientists to refer to a wide range of phenomena in which in an image is presented but not perceived by an observer because of the presentation of a second image. There are several different kinds of masking, many of them relatively intuitive and unsurprising. But one surprising and important type of masking is called Object Substitution Masking. It has been a focus of research in vision science since it was discovered, relatively recently, around 1997 by Enns and Di Lollo.1 This video will demonstrate standard procedures for how to conduct an object substitution experiment, how to analyze the results, and it will also explain the hypothesized causes for this unusual form of masking.

 Sensation and Perception

Mental Rotation

JoVE 10115

Source: Laboratory of Jonathan Flombaum—Johns Hopkins University

Visual mental imagery refers to the ability to conjure images in one’s mind’s eye. This allows people to process visual material above and beyond the constraints of a current point-of-view; for example, a person could imagine, using their mind’s eye, how something might look in a different color, or what it would look like if it were made from a different material or rotated and seen from a different perspective. Mental imagery seems to support important human behaviors in many contexts. For example, people report visualizing routes and maps when planning a route or giving directions. They report visualizing movements, such as swinging a bat, to prepare for an actual action. They also report the mental rotation of objects in order to consider how an object might fit into a receptacle or clear a barrier. This video demonstrates how to use the mental rotation procedure in order to investigate visual mental imagery.

 Cognitive Psychology

Eye Exam

JoVE 10149

Source: Richard Glickman-Simon, MD, Assistant Professor, Department of Public Health and Community Medicine, Tufts University School of Medicine, MA

Proper evaluation of the eyes in a general practice setting involves vision testing, orbit inspection, and ophthalmoscopic examination. Before beginning the exam, it is crucial to be familiar with the anatomy and physiology of the eye. The upper eyelid should be slightly over the iris, but it shouldn't cover the pupil when open; the lower lid lies below the iris. The sclera normally appears white or slightly buff in color. The appearance of conjunctiva, a transparent membrane covering the anterior sclera and the inner eyelids, is a sensitive indicator of ocular disorders, such as infections and inflammation. The tear-producing lacrimal gland lies above and lateral to the eyeball. Tears spread down and across the eye to drain medially into two lacrimal puncta before passing into the lacrimal sac and nasolacrimal duct to the nose. The iris divides the anterior from the posterior chamber. Muscles of the iris control the size of the pupil, and muscles of the ciliary body behind it control the focal length of the lens. The ciliary body also produces aqueous humor, which largely determines intraocular pressure (Figure 1). Cranial nerve

 Physical Examinations II

Just-noticeable Differences

JoVE 10229

Source: Laboratory of Jonathan Flombaum—Johns Hopkins University

Psychophysics is a branch of psychology and neuroscience that tries to explain how physical quantities are translated into neural firing and mental representations of magnitude. One set of questions in this area pertains to just-noticeable differences (JND): How much does something need to change in order for the change to be perceivable? To pump intuitions about this, consider the fact that small children grow at an enormous rate, relatively speaking, but one rarely notices growth taking place on a daily basis. However, when the child returns from sleep-away camp or when a grandparent sees the child after a prolonged absence, just a few weeks of growing is more than perceptible. It can seem enormous! Changes in height are only noticed after an absence because the small changes that take place on a day-to-day basis are too small to be perceivable. But after an absence, many small changes add up. So how much growth needs to take place to be noticeable? The minimal amount is the JND. Psychologists and neuroscientists measure JND in many domains. How much brighter does a light need to be to be noticed? How much louder does a sound need to be? They often obtain the measurements by employing a forced-choice paradigm. This video w

 Sensation and Perception

Measuring Grey Matter Differences with Voxel-based Morphometry: The Musical Brain

JoVE 10299

Source: Laboratories of Jonas T. Kaplan and Sarah I. Gimbel—University of Southern California

Experience shapes the brain. It is well understood that our brains are different as a result of learning. While many experience-related changes manifest themselves at the microscopic level, for example by neurochemical adjustments in the behavior of individual neurons, we may also examine anatomical changes to the structure of the brain at a macroscopic level. One famous example of this kind of change comes from the case of the London taxi drivers, who along with learning the complex routes of the city show larger volume in the hippocampus, a brain structure known to play a role in navigational memory.1 Many traditional methods of examining brain anatomy require painstaking tracing of anatomical regions of interest in order to measure their size. However, using modern neuroimaging techniques, we can now compare the anatomy of the brains across groups of people using automated algorithms. While these techniques do not avail themselves of the sophisticated knowledge that human neuroanatomists may bring to the task, they are quick, and sensitive to very small differences in anatomy. In a structural magnetic resonance image of the brain, the intensity of each volumetric pixel, or voxel, relat


A Visual Description of the Dissection of the Cerebral Surface Vasculature and Associated Meninges and the Choroid Plexus from Rat Brain

1Division of Neurotoxicology, National Center for Toxicological Research, 2Division of Personalized Nutrition and Medicine, National Center for Toxicological Research, 3Office of Planning, Finance, and Information Technology, National Center for Toxicological Research

JoVE 4285



JoVE 10280

Source: Laboratory of Jonathan Flombaum—Johns Hopkins University

Human vision depends on light-sensitive neurons that are arranged in the back of the eye on a tissue called the retina. The neurons, called the rods and cones because of their shapes, are not uniformly distributed on the retina. Instead, there is a region in the center of the retina called the macula where cones are densely packed, and especially so in a central sub-region of the macula called the fovea. Outside the fovea there are virtually no cones, and rod density decreases considerably with greater distance from the fovea. Figure 1 schematizes this arrangement. This kind of arrangement is also replicated in the visual cortex: Many more cells represent stimulation at the fovea compared to the periphery. Figure 1. Schematic depiction of the human eye and the distribution of light-sensitive receptor cells on the retina. The pupil is the opening in the front of the eye that allows light to enter. Light is then focused onto the retina, a neural tissue in the back of the eye that is made of rods and cones, light-sensitive cells. At the center of the retina is the macula, and in

 Sensation and Perception

Electrode Positioning and Montage in Transcranial Direct Current Stimulation

1Headache & Orofacial Pain Effort (H.O.P.E.), Biologic & Material Sciences, School of Dentistry, University of Michigan, 2Laboratory of Neuromodulation, Department of Physical Medicine & Rehabilitation, Spaulding Rehabilitation Hospital and Massachusetts General Hospital, Harvard Medical School, 3Charité, University Medicine Berlin, 4Department of Biomedical Engineering, The City College of New York

JoVE 2744


Measuring Reaction Time and Donders' Method of Subtraction

JoVE 10087

Source: Laboratory of Jonathan Flombaum—Johns Hopkins University

The ambition of experimental psychology is to characterize the mental events that support the human ability to solve problems, perceive the world, and turn thoughts into words and sentences. But people cannot see or feel those mental events; they cannot be weighed, combined in test tubes, or grown in a dish. Wanting to study mental life, nonetheless, Franciscus Donders, a Dutch ophthalmologist in the early 1800s, came up with a property that he could measure—even back then: he measured the time it took for human subjects to perform simple tasks, reasoning that he could treat those measurements as proxies for the time it takes to complete the unobservable mental operations involved. In fact, Donders went one step further, developing a basic experimental paradigm known as the Method of Subtraction. It simply asks a researcher to design two tasks that are identical in nearly every way, excepting a mental operation hypothesized to be involved in one of the tasks and omitted in the other. The researcher then measures the time it takes to complete each task, and by subtracting the outcomes, he extracts an estimate of the time it takes to execute the one mental operation of interest. In this way, the method allows a researcher

 Cognitive Psychology

Non-invasive Imaging and Analysis of Cerebral Ischemia in Living Rats Using Positron Emission Tomography with 18F-FDG

1W. M. Keck Center for Transgene Research, University of Notre Dame, 2Department of Chemistry and Biochemistry, University of Notre Dame, 3Notre Dame Integrated Imaging Facility, University of Notre Dame, 4Department of Biological Sciences, University of Notre Dame, 5Harper Cancer Research Institute, University of Notre Dame

JoVE 51495


Flat-floored Air-lifted Platform: A New Method for Combining Behavior with Microscopy or Electrophysiology on Awake Freely Moving Rodents

1Neuroscience Center, University of Helsinki, 2Neurotar LTD, 3A. I. Virtanen Institute for Molecular Sciences, University of Eastern Finland, 4Laboratory Animal Center, University of Helsinki

JoVE 51869


Description of a Novel, Surgically Implanted Neuromodulatory Technique Known As Bilateral Epidural Prefrontal Cortical Stimulation (Epcs) for Treatment-Resistant Depression (TRD)

1Department of Psychiatry and Behavioral Sciences, Medical University of South Carolina, 2Department of Neurosciences, Medical University of South Carolina, 3Ralph H. Johnson VA Medical Center, 4Department of Psychiatry and Behavioral Sciences, Stanford University, 5American University of Beirut Medical Center

Video Coming Soon

JoVE 56043

 JoVE In-Press

Generation and On-Demand Initiation of Acute Ictal Activity in Rodent and Human Tissue

1Division of Fundamental Neurobiology, Krembil Research Institute, 2Institute of Medical Science, Faculty of Medicine, University of Toronto, 3Institute of Biomaterials and Biomedical Engineering, University of Toronto, 4Division of Neurosurgery, Department of Surgery, University of Toronto, 5Division of Neurology, Department of Medicine, University of Toronto, 6Department of Physiology, University of Toronto

Video Coming Soon

JoVE 57952

 JoVE In-Press

The Use of Magnetic Resonance Spectroscopy as a Tool for the Measurement of Bi-hemispheric Transcranial Electric Stimulation Effects on Primary Motor Cortex Metabolism

1Department of Psychology, University of Montréal, 2Montreal Neurological Institute, McGill University, 3Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota

JoVE 51631


Extracellular Recording of Neuronal Activity Combined with Microiontophoretic Application of Neuroactive Substances in Awake Mice

1Auditory Neuroscience Laboratory, Institute of Neuroscience of Castilla y León, University of Salamanca, 2Neural Systems Laboratory, Institute for Systems Research, University of Maryland, 3Medical Research Council Institute of Hearing Research, 4Department of Cell Biology and Pathology, Faculty of Medicine, University of Salamanca

JoVE 53914


Isolation of Adult Spinal Cord Nuclei for Massively Parallel Single-nucleus RNA Sequencing

1Spinal Circuits and Plasticity Unit, National Institute of Neurological Disorders and Stroke, 2Bioinformatics Section, Information Technology Program, National Institute of Neurological Disorders and Stroke, 3Laboratory of Cochlear Development, National Institute on Deafness and Other Communication Disorders, 4Single Cell Analysis Facility, Frederick National Laboratory

JoVE 58413


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