Psychophysics: The science dealing with the correlation of the physical characteristics of a stimulus, e.g., frequency or intensity, with the response to the stimulus, in order to assess the psychologic factors involved in the relationship.Sensory Aids: Devices that help people with impaired sensory responses.Sensory Thresholds: The minimum amount of stimulus energy necessary to elicit a sensory response.Discrimination (Psychology): Differential response to different stimuli.Photic Stimulation: Investigative technique commonly used during ELECTROENCEPHALOGRAPHY in which a series of bright light flashes or visual patterns are used to elicit brain activity.Refractory Period, Psychological: A delayed response interval occurring when two stimuli are presented in close succession.Visual Perception: The selecting and organizing of visual stimuli based on the individual's past experience.Differential Threshold: The smallest difference which can be discriminated between two stimuli or one which is barely above the threshold.Form Perception: The sensory discrimination of a pattern shape or outline.Motion Perception: The real or apparent movement of objects through the visual field.Contrast Sensitivity: The ability to detect sharp boundaries (stimuli) and to detect slight changes in luminance at regions without distinct contours. Psychophysical measurements of this visual function are used to evaluate visual acuity and to detect eye disease.Pattern Recognition, Visual: Mental process to visually perceive a critical number of facts (the pattern), such as characters, shapes, displays, or designs.Vision, Low: Vision considered to be inferior to normal vision as represented by accepted standards of acuity, field of vision, or motility. Low vision generally refers to visual disorders that are caused by diseases that cannot be corrected by refraction (e.g., MACULAR DEGENERATION; RETINITIS PIGMENTOSA; DIABETIC RETINOPATHY, etc.).Models, Psychological: Theoretical representations that simulate psychological processes and/or social processes. These include the use of mathematical equations, computers, and other electronic equipment.Depth Perception: Perception of three-dimensionality.Signal Detection, Psychological: Psychophysical technique that permits the estimation of the bias of the observer as well as detectability of the signal (i.e., stimulus) in any sensory modality. (From APA, Thesaurus of Psychological Index Terms, 8th ed.)ReadingPerceptual Masking: The interference of one perceptual stimulus with another causing a decrease or lessening in perceptual effectiveness.Visual Cortex: Area of the OCCIPITAL LOBE concerned with the processing of visual information relayed via VISUAL PATHWAYS.Color Perception: Mental processing of chromatic signals (COLOR VISION) from the eye by the VISUAL CORTEX where they are converted into symbolic representations. Color perception involves numerous neurons, and is influenced not only by the distribution of wavelengths from the viewed object, but also by its background color and brightness contrast at its boundary.Vision Tests: A series of tests used to assess various functions of the eyes.Models, Neurological: Theoretical representations that simulate the behavior or activity of the neurological system, processes or phenomena; includes the use of mathematical equations, computers, and other electronic equipment.Fixation, Ocular: The positioning and accommodation of eyes that allows the image to be brought into place on the FOVEA CENTRALIS of each eye.Orientation: Awareness of oneself in relation to time, place and person.Auditory Perception: The process whereby auditory stimuli are selected, organized, and interpreted by the organism.Perception: The process by which the nature and meaning of sensory stimuli are recognized and interpreted.Visual Pathways: Set of cell bodies and nerve fibers conducting impulses from the eyes to the cerebral cortex. It includes the RETINA; OPTIC NERVE; optic tract; and geniculocalcarine tract.Vision, Ocular: The process in which light signals are transformed by the PHOTORECEPTOR CELLS into electrical signals which can then be transmitted to the brain.Vision Disparity: The difference between two images on the retina when looking at a visual stimulus. This occurs since the two retinas do not have the same view of the stimulus because of the location of our eyes. Thus the left eye does not get exactly the same view as the right eye.Visual Fields: The total area or space visible in a person's peripheral vision with the eye looking straightforward.Cues: Signals for an action; that specific portion of a perceptual field or pattern of stimuli to which a subject has learned to respond.Acoustic Stimulation: Use of sound to elicit a response in the nervous system.Vision, Binocular: The blending of separate images seen by each eye into one composite image.Electroretinography: Recording of electric potentials in the retina after stimulation by light.Discrimination Learning: Learning that is manifested in the ability to respond differentially to various stimuli.Attention: Focusing on certain aspects of current experience to the exclusion of others. It is the act of heeding or taking notice or concentrating.Reaction Time: The time from the onset of a stimulus until a response is observed.Visual Field Tests: Method of measuring and mapping the scope of vision, from central to peripheral of each eye.Visual Acuity: Clarity or sharpness of OCULAR VISION or the ability of the eye to see fine details. Visual acuity depends on the functions of RETINA, neuronal transmission, and the interpretative ability of the brain. Normal visual acuity is expressed as 20/20 indicating that one can see at 20 feet what should normally be seen at that distance. Visual acuity can also be influenced by brightness, color, and contrast.Magnetic Resonance Imaging: Non-invasive method of demonstrating internal anatomy based on the principle that atomic nuclei in a strong magnetic field absorb pulses of radiofrequency energy and emit them as radiowaves which can be reconstructed into computerized images. The concept includes proton spin tomographic techniques.Brain Mapping: Imaging techniques used to colocalize sites of brain functions or physiological activity with brain structures.Psychomotor Performance: The coordination of a sensory or ideational (cognitive) process and a motor activity.Time Factors: Elements of limited time intervals, contributing to particular results or situations.Neurons: The basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the NERVOUS SYSTEM.

*  ATTENTION, PERCEPTION, AND PSYCHOPHYSICS | Years 1966-2015 | Print ISSN 1943-3921 | PSC Reprint and Publisher's Backstock

ATTENTION, PERCEPTION, AND PSYCHOPHYSICS. Years 1966-2015. Print ISSN 1943-3921. Reprint. Back volumes and back issues available from Periodicals Service Company (PSC).

*  The International Society for Psychophysics

The 33rd annual meeting of the international society for Psychophysics will be held in Fukuoka, Japan, 22-26 October 2017. Please note down the key dates of the conference: Friday, 7 […]. ...

*  Aerial perspective - Wikipedia

The ability of a person with normal visual acuity to see fine details is determined by his or her contrast sensitivity.[1] Contrast sensitivity is the reciprocal of the smallest contrast for which a person can see a sine-wave grating. A person's contrast sensitivity function is contrast sensitivity as a function of spatial frequency. Normally, peak contrast sensitivity is at about 4 cycles per degree of visual angle. At higher spatial frequencies, comprising finer and finer lines, contrast sensitivity decreases, until at about 40 cycles per degree even the brightest of bright lines and the darkest of dark lines cannot be seen.. The high spatial frequencies in an image give it its fine details.[2] Reducing the contrast of an image reduces the visibility of these high spatial frequencies because contrast sensitivity for them is already poor. This is how a reduction of contrast can reduce the clarity of an image - by removing its fine details.. It is important to emphasize that reducing the ...

*  Capabilities of monkey cortical cells in spatial-resolution tasks. - Nuffield Department of Clinical Neurosciences

The performance of individual neurons in monkey striate cortex has been examined in three spatial-resolution tasks by making microelectrode recordings from single cells in anaesthetized, paralyzed animals. The statistical reliability of responses from cells was used to estimate threshold levels of performance. For each task (resolution acuity for high-contrast gratings, discrimination of gratings varying in spatial frequency, and localization ability, i.e., discrimination of spatial phase), performance approaching psychophysical thresholds was obtained from single cortical cells. The receptive-field organization underlying localization performance was examined in detail by the use of a linear model that relates localization ability to the sensitivity of the receptive field to luminance contrast. Calculations from this model agree well with direct measurements of localization performance and are comparable with psychophysical measurements of hyperacuity. Though it has been suggested that cells with

*  Psychophysics of Haptic Interaction - Projects - Microdynamic Systems Laboratory

Bertram Unger, Roberta Klatzky, Ralph Hollis, Alex Nicolaidis, Peter Berkelman, Andy Thompson, Vinithra Varadharajan, Susan Lederman (Queens University), and Andy Moore. Quantitative comparisons of human subjects performing peg-in-hole experiments with real, virtual, and real-remote haptic environments. In the Microdynamics Systems Laboratory we are interested in measuring how much reality a haptic device can deliver (its fidelity). We have used our magnetic levitation haptic interface to perform a set of psychophysical experiments that examine the way in which users interact with real and virtual haptic worlds. For an introduction, an elementary discussion of haptics can be found in the encyclopedia article 'Haptics' by Ralph Hollis. Previous investigations of haptic fidelity have mostly focused on engineering qualities related to device kinematics and dynamics such as frequency response or position bandwidth. In contrast, psychophysical studies of haptic fidelity apply careful metrics to user ...

*  Liz Whitchurch

Liz earned a BS in Chemistry/Biochemistry at Utah State University (1998) and a PhD in Biology at the University of Oregon (2006). As a doctoral student, she examined audiovisual integration in the barn owl head saccade behavior, and she measured single cell responses to visual and auditory stimuli in the optic tectum and external nucleus of the inferior colliculus of anesthetized barn owls. From 2007-2010, Liz stayed on at the University of Oregon as an adjunct instructor (BIO 353 - Sensory Physiology) and as a postdoctoral researcher. Her research time was split between the labs of Terry Takahashi and Bill Roberts. As a postdoc in the Takahashi Lab, Liz mentored various undergraduate researchers on projects ranging from human psychophysics to barn owl awake-behaving tetrode measurements. Her project in the Roberts Lab involved confocal imaging and scanning electron microscopy of the frog saccule, looking for morphologically and physiologically distinct subpopulations of hair cells in this ... W page.htm

*  Recent Articles | Immunology And Neuroscience | The Scientist Magazine®| Page 21

The UCLA neurobiologist uses computational modeling, in vitro electrophysiology, and human psychophysics experiments to explore how neurons and the brain as a whole perceive and respond to time.. 0 Comments. ...,11/tags/immunology,neuroscience/pageNo/21/

*  Profile Articles - Human Genome Project, neuroscience and genetics & genomics | The Scientist Magazine®

The UCLA neurobiologist uses computational modeling, in vitro electrophysiology, and human psychophysics experiments to explore how neurons and the brain as a whole perceive and respond to time.. 0 Comments. ...,11,9/tags/Human-Genome-Project,neuroscience,genetics--amp--genomics/

*  Citation Machine: Journal Of Experimental Psychology: Human Perception And Performance format citation generator for...

Citation Machine™ helps students and professionals properly credit the information that they use. Cite your multivolume work in Journal of Experimental Psychology: Human Perception and Performance format for free.

*  Normalization Model of Attention: Theory, Psychophysics, and Neuroimaging - David Heeger

Attention has played a central role in perception research since the dawn of experimental psychology. Over the past 20 years, the neurophysiological basis of vi...

*  Visual Mechanisms of Motion Perception and Analysis. - SURE

Derrington, Andrew, M, Allen, Harriet, A and Delicato, Louise (2004) Visual Mechanisms of Motion Perception and Analysis. Annual Review of Psychology, 55. pp. 181-205. ISSN 0066-4308 Full text not available from this repository ...

*  Citation Machine: Experimental Psychology format citation generator for letter

Citation Machine™ helps students and professionals properly credit the information that they use. Cite your letter in Experimental Psychology format for free.

*  Brevard College experimental psychology

Find info concerning Brevard College experimental psychology. You can start working in a high-paying field with just an associates or a bachelors degree. To begin, browse accredited college degree programs and certificate courses online.

*  Integration of shape information from vision and touch: Optimal perception and neural correlates

Helbig, H. B., Ricciardi, E., Pietrini, P., & Ernst, M. O. (2006). Integration of shape information from vision and touch: Optimal perception and neural correlates. Journal of Vision, 6(6), 179. doi:10.1167/6.6. ...

*  Journal of experimental psychology. Human perception and performance

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*  P30 - Core Grant for Vision Research - P Iuvone

Continued support is requested forth NEI Core Grant for Vision Research at Emory University and neighboring Atlanta institutions. This Core Center Grant renewal...

*  Scientific Psychology Series - Routledge

By Louis Narens. This book is designed to be an introduction to the theories of measurement and meaningfulness, and not a comprehensive study of those topics. A major theme of this book is the psychophysical measurement of subjective intensity. This has been a subject of intense interest in psychology from the very…. Paperback - 2013-10-31 ...

*  Structures As Patterns and Textures: The Elements Of Design Part IV - Vanseo Design

Visual activity across a surface is a texture when the structure forming the texture is based on irregular and random relationships over given areas. Textures are organic and natural. The size of the objects or lines forming the texture may vary. The distance between them may vary. The density of the structure may vary. This variety leads to a perception of organic, natural, or random structures in a texture.. Textures are physical. We can touch them. We can feel them. They can be smooth or rough, hard or soft. Naturally in web design we can't actually create this physical quality. We can only create the perception of this physical quality. When we work in a 2-dimensional format we create implied texture. Done well your audience will be able to imagine how your texture will feel.. This physical quality gives texture a sense of realism. Textures add depth, a 3rd dimension to the 2-dimensional format of the screen in an organic way. This connection to the physical world can give a greater sense of ...

*  Patent US7433728 - Dynamic metal immunity by hysteresis - Google Patents

Apparatus is provided for tracking an object in a body of a patient in the presence of an interfering article. A set of one or more radiators are adapted to generate an energy field at a fundamental frequency in a vicinity of the object. A position sensor, fixed to the object, is adapted to generate a signal responsive to the energy field. A control unit has access to a database of one or more harmonic frequency patterns associated with one or more respective specific types of interfering articles. The control unit is adapted to (a) receive the signal, (b) detect a pattern of harmonic frequencies of the fundamental frequency present in the signal responsive to an interaction of the interfering article with the energy field, (c) compare the pattern to harmonic frequency patterns stored in the database, (d) identify the interfering article responsive to the comparison, (e) correct the signal responsive to the identification of the interfering article and a magnitude of one or more of the harmonic,274,924

*  WaveLight® Refractive Flap Accuracy Study - Full Text View -

Contrast sensitivity (ie, the ability to detect slight changes in luminance before they become indistinguishable) was assessed binocularly with distance manifest correction in place and uncorrected. Contrast sensitivity was assessed at spatial frequencies of 3, 6, 12, and 18 cycles per degree (cpd), where 3.0 cpd = A, 6.0 cpd = B, 12.0 cpd = C, and 18.0 cpd = D. Raw scores were log transformed. A higher numeric value represents better contrast sensitivity. Both eyes contributed to the analysis ..."Refractive Errors"&rank=11

*  Planned giving supports HudsonAlpha and benefits donors - HudsonAlpha Institute for Biotechnology

The value of planned giving took center stage this month. Sharon Doviet and Chris Russell hosted a reception at their home, inviting friends, clients and colleagues to learn more about the HudsonAlpha Institute for Biotechnology. During the event, the couple also announced their decision to include HudsonAlpha in their will, committing at least $250,000 to the HudsonAlpha Foundation.. "Sharon and I are excited to invest in nonprofits where the impact of our giving will compound and grow over time," said Russell, a financial advisor at Cadence Bank and a member of HudsonAlpha's Professional Advisor Council. "HudsonAlpha is becoming a world-class player in biotechnology. This is work that will improve lives for our families and friends now, and for our children and the broader community for many years ahead.". During a brief presentation, guests heard from Rick Myers, PhD, president and science director; Howard Jacob, PhD, executive vice president for genomic medicine; and Jim Hudson, HudsonAlpha ...

*  Experimental Psychology - MADOC

Erdfelder, Edgar und Bayen, Ute J. und Greenwald, Anthony G. und Humphreys, Glyn und Kerzel, Dirk und Koch, Iring und Leuthold, Hartmut und Meiser, Thorsten und Musch, Jochen und Rothermund, Klaus ...

*  Vision Research Core Grant - John Werner

This application seeks five years of continued support for an NEI Core Grant that has facilitated the research efforts of vision scientists at the University of...

*  Special relativity: kinematics - Scholarpedia

We shall presently discuss two of the most fundamental phenomena of SR, length contraction and time dilation: moving rods shrink, and moving clocks go slow, both by a \(\gamma\) factor. Does the observer's eye see these effects by the claimed amount? No. Because of the finite speed of light, what an observer sees at one instant is a composite of events that occurred progressively earlier as they occurred farther away. No observer can get an instantaneous view of the moving rod. What he actually sees, his world-picture, is irrelevant for our present purposes. The concept that plays a pervasive role in special relativity is that of a world-map. As the name implies, this may be thought of as a (3-dimensional) map of events, namely those constituting an observer's instantaneous 3-space \(t = t_0\ .\) The main class of observers one considers in SR are 'inertial observers' -- observers at rest in some inertial frame \((x,y,z,t)\ ,\) say at its spatial origin. A world-map could be produced by having ...

*  Axio Observer - Your open and flexible inverted microscope platform

Axio Observer is your inverted research stand for demanding multimodal imaging of living and fixed specimens. It creates the optimal environment for a whole range of samples to deliver reliable, reproducible data. A wealth of technologies and refinements suppors your experiments optimally.

Korte's law: In psychophysics, Korte's law, also known more completely as Korte's third law of apparent motion, is an observation relating the phenomenon of apparent motion to the distance and duration between two successively presented stimuli. It was originally proposed in 1915 by Adolf Korte.Braille technology: Braille technology is assistive technology which allows blind or visually impaired people to do common tasks such as writing, browsing the Internet, typing in Braille and printing in text, engaging in chat, downloading files, music, using electronic mail, burning music, and reading documents. It also allows blind or visually impaired students to complete all assignments in school as the rest of sighted classmates and allows them take courses online.Percolation threshold: Percolation threshold is a mathematical concept related to percolation theory, which is the formation of long-range connectivity in random systems. Below the threshold a giant connected component does not exist; while above it, there exists a giant component of the order of system size.Psychological refractory period: The term psychological refractory period (PRP) refers to the period of time during which the response to a second stimulus is significantly slowed because a first stimulus is still being processed. This delay in response time when one is required to divide attention can exhibit a negative effect that is evident in many fields of study.Just-noticeable difference: In the branch of experimental psychology focused on sensation and perception, psychophysics, a just-noticeable difference or JND is the amount something must be changed in order for a difference to be noticeable, detectable at least half the time. Weber's Law of Just Noticeable Difference, University of South Dakota: http://apps.Biological motion: Biological motion is a term used by social and cognitive neuroscientists to refer to the unique visual phenomenon of a moving, animate object. Often, the stimuli used in biological motion experiments are just a few moving dots that reflect the motion of some key joints of the moving organism.Low vision assessment: Low vision is both a subspeciality and a condition. Optometrists and Ophthalmologists after their training may undergo further training in Low vision assessment and management.Stereopsis: Stereopsis (from the Greek στερεο- [meaning "solid", and ὄψις] opsis, "appearance, [[visual perception|sight") is a term that is most often used to refer to the perception of depth and 3-dimensional structure obtained on the basis of visual information deriving from two eyes by individuals with normally developed binocular vision.Vigilance (psychology): In modern psychology, vigilance, also termed sustained concentration, is defined as the ability to maintain concentrated attention over prolonged periods of time.Warm, J.Spalding MethodLandolt CCanon EOS 5Auditory scene analysis: In psychophysics, auditory scene analysis (ASA) is a proposed model for the basis of auditory perception. This is understood as the process by which the human auditory system organizes sound into perceptually meaningful elements.Immaculate perception: The expression immaculate perception has been used in various senses by various philosophers.Meridian (perimetry, visual field): Meridian (plural: "meridians") is used in perimetry and in specifying visual fields. According to IPS Perimetry Standards 1978 (2002): "Perimetry is the measurement of [an observer's] visual functions ...Cue stick: A cue stick (or simply cue, more specifically pool cue, snooker cue, or billiards cue), is an item of sporting equipment essential to the games of pool, snooker and carom billiards. It is used to strike a ball, usually the .Binocular vision: Binocular vision is vision in which creatures having two eyes use them together. The word binocular comes from two Latin roots, bini for double, and oculus for eye.Gary H. Posner: Gary H. Posner (born c.Plaque-forming unit: In virology, a plaque-forming unit (PFU) is a measure of the number of particles capable of forming plaques per unit volume, such as virus particles. It is a functional measurement rather than a measurement of the absolute quantity of particles: viral particles that are defective or which fail to infect their target cell will not produce a plaque and thus will not be counted.LogMAR chart: A LogMAR chart comprises rows of letters and is used by ophthalmologists and vision scientists to estimate visual acuity. This chart was developed at the National Vision Research Institute of Australia in 1976, and is designed to enable a more accurate estimate of acuity as compared to other charts (e.HyperintensityTemporal analysis of products: Temporal Analysis of Products (TAP), (TAP-2), (TAP-3) is an experimental technique for studyingHSD2 neurons: HSD2 neurons are a small group of neurons in the brainstem which are uniquely sensitive to the mineralocorticosteroid hormone aldosterone, through expression of HSD11B2. They are located within the caudal medulla oblongata, in the nucleus of the solitary tract (NTS).

(1/3601) On the neural correlates of visual perception.

Neurological findings suggest that the human striate cortex (V1) is an indispensable component of a neural substratum subserving static achromatic form perception in its own right and not simply as a central distributor of retinally derived information to extrastriate visual areas. This view is further supported by physiological evidence in primates that the finest-grained conjoined representation of spatial detail and retinotopic localization that underlies phenomenal visual experience for local brightness discriminations is selectively represented at cortical levels by the activity of certain neurons in V1. However, at first glance, support for these ideas would appear to be undermined by incontrovertible neurological evidence (visual hemineglect and the simultanagnosias) and recent psychophysical results on 'crowding' that confirm that activation of neurons in V1 may, at times, be insufficient to generate a percept. Moreover, a recent proposal suggests that neural correlates of visual awareness must project directly to those in executive space, thus automatically excluding V1 from a related perceptual space because V1 lacks such direct projections. Both sets of concerns are, however, resolved within the context of adaptive resonance theories. Recursive loops, linking the dorsal lateral geniculate nucleus (LGN) through successive cortical visual areas to the temporal lobe by means of a series of ascending and descending pathways, provide a neuronal substratum at each level within a modular framework for mutually consistent descriptions of sensory data. At steady state, such networks obviate the necessity that neural correlates of visual experience project directly to those in executive space because a neural phenomenal perceptual space subserving form vision is continuously updated by information from an object recognition space equivalent to that destined to reach executive space. Within this framework, activity in V1 may engender percepts that accompany figure-ground segregations only when dynamic incongruities are resolved both within and between ascending and descending streams. Synchronous neuronal activity on a short timescale within and across cortical areas, proposed and sometimes observed as perceptual correlates, may also serve as a marker that a steady state has been achieved, which, in turn, may be a requirement for the longer time constants that accompany the emergence and stability of perceptual states compared to the faster dynamics of adapting networks and the still faster dynamics of individual action potentials. Finally, the same consensus of neuronal activity across ascending and descending pathways linking multiple cortical areas that in anatomic sequence subserve phenomenal visual experiences and object recognition may underlie the normal unity of conscious experience.  (+info)

(2/3601) Transient and permanent deficits in motion perception after lesions of cortical areas MT and MST in the macaque monkey.

We examined the nature and the selectivity of the motion deficits produced by lesions of extrastriate areas MT and MST. Lesions were made by injecting ibotenic acid into the representation of the left visual field in two macaque monkeys. The monkeys discriminated two stimuli that differed either in stimulus direction or orientation. Direction and orientation discrimination were assessed by measuring thresholds with gratings and random-dots placed in the intact or lesioned visual fields. At the start of behavioral testing, we found pronounced, motion-specific deficits in thresholds for all types of moving stimuli, including pronounced elevations in contrast thresholds and in signal-to-noise thresholds measured with moving gratings, as well as deficits in direction range thresholds and motion coherence measured with random-dot stimuli. In addition, the accuracy of direction discrimination was reduced at smaller spatial displacements (i.e. step sizes), suggesting an increase in spatial scale of the residual directional mechanism. Subsequent improvements in thresholds were seen with all motion stimuli, as behavioral training progressed, and these improvements occurred only with extensive behavioral testing in the lesioned visual field. These improvements were particularly pronounced for stimuli not masked by noise. On the other hand, deficits in the ability to extract motion from noisy stimuli and in the accuracy of direction discrimination persisted despite extensive behavioral training. These results demonstrate the importance of areas MT and MST for the perception of motion direction, particularly in the presence of noise. In addition, they provide evidence for the importance of behavioral training for functional recovery after cortical lesions. The data also strongly support the idea of functional specialization of areas MT and MST for motion processing.  (+info)

(3/3601) Psychophysics of remembering.

We present a new model of remembering in the context of conditional discrimination. For procedures such as delayed matching to sample, the effect of the sample stimuli at the time of remembering is represented by a pair of Thurstonian (normal) distributions of effective stimulus values. The critical assumption of the model is that, based on prior experience, each effective stimulus value is associated with a ratio of reinforcers obtained for previous correct choices of the comparison stimuli. That ratio determines the choice that is made on the basis of the matching law. The standard deviations of the distributions are assumed to increase with increasing retention-interval duration, and the distance between their means is assumed to be a function of other factors that influence overall difficulty of the discrimination. It is a behavioral model in that choice is determined by its reinforcement history. The model predicts that the biasing effects of the reinforcer differential increase with decreasing discriminability and with increasing retention-interval duration. Data from several conditions using a delayed matching-to-sample procedure with pigeons support the predictions.  (+info)

(4/3601) Detection of vibration transmitted through an object grasped in the hand.

A tool or probe often functions as an extension of the hand, transmitting vibrations to the hand to produce a percept of the object contacting the tool or probe. This paper reports the psychophysical results of a combined psychophysical and neurophysiological study of the perception of vibration transmitted through a cylinder grasped in the hand. In the first part of the psychophysical study, 19 subjects grasped a cylinder, 32 mm diam, with an embedded motor that caused vibration parallel to the axis of the cylinder. The relationship between threshold and frequency was the traditional U-shaped function with a minimum between 150 and 200 Hz. Except a study by Bekesy in which subjects grasped a rod that vibrated parallel to the skin surface, thresholds above 20 Hz were lower and the slopes were steeper than any reported previously. Thresholds were <0.01 microm in some subjects. Data from both the psychophysical and the neurophysiological studies suggest that detection performance at frequencies >20 Hz was based on activity in Pacinian afferents. The extreme sensitivity compared with previous reports may have resulted from differences in contact area, direction of vibration, contact force, and the shape of the stimulus probe. The effects of each of these variables were studied. At 40 and 300 Hz (frequencies near the lower and upper end of the Pacinian range) thresholds were 9.8 and 18.5 dB (68 and 88%) lower, respectively, when subjects grasped the cylinder than when a 1-mm-diam probe vibrated perpendicular to the skin. These differences were accounted for as follows: 1) thresholds at a single fingerpad obtained with the large cylindrical surface were, on average, 20 and 60% lower, respectively, than thresholds with the punctate probe; 2) thresholds at the palm were, on average, 15 and 40% lower, respectively, than at the fingerpads; 3) thresholds obtained when the subjects grasped the cylinder averaged 40 and 20% less, respectively, than when the cylinder contacted only the palm; 4) thresholds with the cylinder contacting two fingers were 10 and 30% lower, respectively, than thresholds with the cylinder contacting a single finger; and 5) thresholds with vibration parallel to the skin surface were, on average, 10 and 30% lower, respectively, than thresholds with vibration perpendicular to the skin. Contact force, which was varied from 0.05 to 1.0 N, had no effect.  (+info)

(5/3601) Effect of spatial attention on the responses of area MT neurons.

This study examines the influence of spatial attention on the responses of neurons in the middle temporal visual area (MT or V5) of extrastriate cortex. Two monkeys were trained to perform a direction-discrimination task. On each trial, two apertures of random-dot stimuli appeared simultaneously at two spatially separated locations; the monkeys were required to discriminate the direction of stimulus motion at one location while ignoring the stimulus at the other location. After extensive training, we recorded the responses of MT neurons in two configurations: 1) Both apertures placed "within" the neuron's receptive field (RF) and 2) one aperture covering the RF while the other was presented at a "remote" location. For each unit we compared the responses to identical stimulus displays when the monkey was instructed to attend to one or the other aperture. The responses of MT neurons were 8.7% stronger, on average, when the monkey attended to the spatial location that contained motion in the "preferred" direction. Attentional effects were equal, on average, in the within RF and remote configurations. The attentional modulations began approximately 300 ms after stimulus onset, gradually increased throughout the trial, and peaked near stimulus offset. An analysis of the neuronal responses on error trials suggests that the monkeys failed to attend to the appropriate spatial location on these trials. The relatively weak attentional effects that we observed contrast strikingly with recent results of Treue and Maunsell, who demonstrated very strong attentional modulations (median effect >80%) in MT in a task that shares many features with ours. Our results suggest that spatial attention alone is not sufficient to induce strong attentional effects in MT even when two competing motion stimuli appear within the RF of the recorded neuron. The difference between our results and those of Treue and Maunsell suggests that the magnitude of the attentional effects in MT may depend critically on how attention is directed to a particular stimulus and on the precise demands of the task.  (+info)

(6/3601) Geometric representation of the mechanisms underlying human curvature detection.

Combined manipulation of blur, line length and contrast reveal two distinct processes involved in curvature detection. When line length is small relative to blur, thresholds are almost directly proportional to blur and independent of line length. When line length is large relative to blur thresholds are directly proportional to line length and independent of blur. The aspect ratio (line length/blur) of curved contours represents a scale-invariant metric which forms the decisive factor in determining curvature performance.  (+info)

(7/3601) Chromatic masking in the (delta L/L, delta M/M) plane of cone-contrast space reveals only two detection mechanisms.

The post-receptoral mechanisms that mediate detection of stimuli in the (delta L/L, delta M/M) plane of color space were characterized using noise masking. Chromatic masking noises of different chromaticities and spatial configurations were used, and threshold contours for the detection of Gaussian and Gabor tests were measured. The results do not show masking that is narrowly-selective for the chromaticity of the noise. On the contrary, our findings suggest that detection of these tests is mediated only by an opponent chromatic mechanism (a red-green mechanism) and a non-opponent luminance mechanism. These results are not consistent with the hypothesis of multiple chromatic mechanisms mediating detection in this color plane [1].  (+info)

(8/3601) Is the rod visual field temporally homogeneous?

Cone vision has been shown to be temporally inhomogeneous across the visual field. In the periphery, contrast sensitivity is lower for low temporal frequencies and higher for high temporal frequencies. Here we ask a similar question for rod vision at mesopic luminances. Isolation is obtained by testing a well documented rod monochromat. We show that the rod visual field exhibits only a modest degree of temporal inhomogeneity.  (+info)

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