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This chapter reviews the physiology of processes devoted to the detection of binocular disparity. The discussions cover disparity detectors; disparity detectors in cats; disparity detectors in primates; subcortical disparity-tuned cells; disparity-detector properties; coding higher-order disparities; visual evoked potentials (VEPs) and binocular vision; and models of disparity processing.

It is well known that the sensory cortex responds to peripheral input, and that sensory stimuli evoke a cortical response. In fact, in cases of myoclonic epilepsy, the response to a peripheral stimulus can be detected using standard electroencephalogram (EEG ) recording. In normal subjects, however, the responses are of much lower amplitude. The normal EEG activity and the normal “noise” in the recording devices are of high enough voltage to mask any evoked response. With the onset of averaging technology, these small potentials became detectable. The procedure is to time-lock a peripheral stimulus to another which triggers the sweep of a computer of average transients. Any evoked potential that recurs with a fixed relationship to this peripheral stimulus is summed by the computer. All non-related potentials, or random waves, are progressively diminished and eventually cancel out. Thus, with adequate averaging, smaller and smaller evoked potentials can be extracted from the background activity.

Mycolonus is a sudden, irregular, jerky movement of a group of muscles. It can be related to hyperexcitability of cerebral neurons, manifested by periodic synchronous EEG discharges (PSDs). If these are cortical, the relationship can be studied using several techniques. The most basic is polygraph recording of both electroencephalogram (EEG) and electromyogram (EMG) events to study any temporal relationship between cortical discharges and muscle movement. In some forms (such as cortical reflex myoclonus), routine somatosensory evoked potential studies can produce giant responses. There are more specialized methods to characterize the temporal relationship between cortical and myoclonic events. One is jerk-locked averaging. Another is jerk-locked evoked potentials. In addition, long-latency reflexes can be recorded. These require specialized arrangements including a triggering device and a backward averaging program (opisthotonic) that permits studying the period preceding the triggering event.

This chapter describes steady-state visual evoked potentials (SSVEPs), slow cortical potentials (SCPs), and brain-computer interfaces (BCIs) based on these signals. SSVEPs are produced by repetitive stimuli (e.g., a flashing light or a pattern-reversing checkerboard) and are focused over occipital cortex. With a rhythmic stimulus, they typically display a peak at the frequency of the stimulus and at several harmonic frequencies. BCIs based on SSVEPs and similar signals can provide relatively robust and rapid communication and have been applied to a variety of applications including word-processing, navigation tasks, and computer games. SCPs are slow, mainly negative, voltage shifts recorded over sensorimotor or frontal cortical areas. They precede and coincide with imagined or actual motor actions or cognitive tasks. With extensive training, people can learn to control SCPs and use them to operate spelling programs and other applications.

In patients with tinnitus, structural and functional brain imaging combined with electro- and magnetoencephalograms have suggested correlations between aspects of tinnitus and brain functioning. Participating brain regions are among others in the auditory cortex, in the limbic system and in the cerebellum. Spontaneous EEG and MEG points to a reduction of alpha-band activity and an increase in delta- and gamma-band activity. The strength of the latter appears to correlate well with tinnitus loudness, whereas that of the alpha- and delta-band relates more to the level of annoyance caused by the tinnitus. The clear changes in spontaneous synchrony in the MEG activity between different neocortical areas in tinnitus patients also suggest wide involvement of brain areas in this disorder.

Visual evoked potentials provide a quantitative measure of the visual system. The function measured includes that of the optic nerve, through the optic chiasm and tract, to the lateral geniculate bodies, and the geniculocalcarine projection to the visual cortex. The use of small-sized stimuli tests the foveal region, emanating primarily from the central fifteen degrees. The most reliable information relates to lesions of the optic nerve, and is derived by individual testing of each eye. An important application of visual evoked responses is as a screen for multiple sclerosis lesions. Abnormalities have also been shown in other conditions such as glaucoma, parkinsonism, and cortical blindness. It can also be used to measure visual acuity in infants. Since the response relies on a visual image reaching the retina, it is important to screen initially for any significant decrease in visual acuity. If possible, this should be corrected. If not, flash stimuli may yield some information, although this may or may not be as sensitive a test.

This chapter describes some of the methods used for testing vision in infants and young children in research and clinical assessment, including behavioural measures from observing eye movements (forced choice preferential looking /habituation), video/photorefraction, and visual evoked potentials (VEP) or visual event related potentials (VERP). It outlines how these methods have been used and compared, including the use of forced-choice preferential looking for acuity testing and acuity measures in preschool children using the Cambridge Crowding Cards, devised in the Visual Development Unit. It describes the subtests from the Atkinson Battery of Child Development for Examining Functional Vision (ABCDEFV), a behavioural battery which assesses children's functional use of sensory, perceptual, and cognitive vision, from birth to five years.

This chapter discusses time series analysis. Topics covered include method of moments, evoked potentials and peristimulus time histogram, univariate spectral analysis, bivariate spectral analysis, prediction, point process spectral estimation, and higher order correlations.

The impetus to study visual ontogenesis and the corresponding plethora of developmental studies have resulted in major advances in our knowledge of the relationship between various aspects of visual perception and maturation of the corresponding anatomical and physiological substrates. The basic requisite in this area of study is to understand normal visual function and its development to optimum visual capacity, as well as to understand the aetiology of abnormal visual development and its detrimental consequences. Normal maturation of the visual pathway is dependent not only upon intrinsic biological factors but upon the infant's ability to sustain normal visual experience. An alternative to the behavioural approach is non-invasive electrophysiology, namely visual evoked potentials (VEPs). An advantage of evoked potential assessment is that, in addition to the ability to test performance for various visual tasks, VEPs can measure visual capacity and maturation at varying stages of processing along the visual pathway from the retina to cortex. In the present overview, application of the VEPs in paediatric neuro ophthalmology is described, together with the various stimulus and recording techniques designed to optimize VEP testing in infants and young children. A practical approach to electrodiagnostic assessment of visual function in paediatric neuro-ophthalmology is presented. Stimulus and recording techniques are outlined and substantial attention is paid to the ‘four-parameter approach’ to VEP assessment for clinical application. The four basic VEP parameters, amplitude, latency, waveform, and topography, are described in detail.

Visual evoked potentials (VEPs) provide an objective technique for monitoring the integrity of visual pathways and have been used to monitor the activity of post-receptoral chromatic mechanisms. The temporal properties of visual processing may now be characterized in terms of VEP integration time, defined as the stimulus duration during which response components are summed to give the highest amplitude VEP. The onset of a luminance-modulated pattern of moderate spatial frequency elicits the largest VEP when the grating appearance is brief, i.e. about 40-60 ms, consistent with predominant activation of transient mechanisms. Likewise, the greatest amplitude chromatic VEPs are obtained with isoluminant coarse L/M gratings when the offset period exceeds the onset duration. This chapter compares L/M tritan integration times by obtaining VEP responses to the onset of two cycles per deg gratings of varying onset durations, in order to characterize the temporal response mechanisms contributing to the two chromatic processing streams.

This chapter discuses various potential recording methods of ophthalmology. The electro-oculogram (EOG) is described as a registration of the increase in the corneoretinal potential caused by an increase of the illumination of the retina. The use of visual evoked potentials (VEPs) are used for the application of the visual pathway conduction, misrouting, and objective visual acuity measurement. The applications and standardized protocol of electroretinograms (ERG) have also been finalized. VEP brain maps are combined with brain-imaging techniques, such as magnetic resonance imaging (MRI) and single photon emission computed tomography (SPECT), to interpret these recordings in ophthalmology.

This chapter examines the tonotopic organization of the human auditory cortex using intracerebrally recorded evoked potentials studied as a function of the anatomical recording site. The sensitivity of a neuronal population to a given frequency is determined from fluctuations in auditory evoked potential (AEP) amplitude between different recording sites in the primary auditory cortex and surrounding secondary areas like the planum temporale. The chapter particularly explores the tonotopic organization of the human auditory cortex in both cerebral hemispheres. In the right hemisphere, clear spectrally organized tonotopic maps wre observed with distinct separations between different frequency-processing regions. AEPs for high frequencies were recorded medially, whereas AEPs for low frequencies were recorded laterally. However, in the left hemisphere, this tonotopic organization was less evident, with different regions involved in the processing of a range of frequencies. The hemisphere-related difference in the processing of tonal frequency is discussed in relation to pitch perception.

This chapter examines the electroencephalographic (EEG) markers of brain activity used to investigate the brain-based timing mechanisms that presumably underlie temporal preparation as manifested in foreperiod effects. These markers are the contingent negative variation (CNV) and the modulation of sensory-evoked potentials. This chapter discusses the implicit timing effects on the CNV, sensory-evoked potentials, and oscillatory activity and describes the models of timing and the neural representation of timing processes.

Evoked potentials are those components of the EEG that arise in response to a stimulus (which may be electric, auditory, visual, etc.). Such signals are usually below the noise level and thus not readily distinguished, and one must use a train of stimuli and signal averaging to improve the signal-to-noise ratio. Single-neuron behavior can be examined through the use of microelectrodes which impale the cells of interest. Through studies of the single cell, one hopes to build models of cell networks that will reflect actual tissue properties.

Behaviourally spontaneous confabulation denotes a particular form of confabulation characterized by confusion of reality. The patients are disoriented and act according to their confabulations. This chapter describes the clinical course of the disorder and shows how the experimental exploration of patients opened ways to study the underlying mechanism in healthy subjects using brain imaging, electrophysiology, and other methods. These studies revealed a distinct mechanism, now called orbitofrontal reality filtering, which depends on the orbitofrontal cortex and parts of the brain’s reward system. It automatically verifies the relation of upcoming thoughts and memories with ongoing reality. Its relevance for children’s sense of reality is discussed. Comparison with single-cell recordings in animals and investigations in patients suggest that the mechanism depends on a phylogenetically old faculty: an orbitofrontal signal akin to the one necessary for behavioural extinction.

Accurate representation of sound onsets is determined by the dynamics of the sound as well as the threshold for sound detection in the auditory system. Fast onset sound of sufficient intensity generally produces the shortest onset latencies and the smallest deviations therein. The threshold for detecting the presence of a sound may include integration of sound energy over a time sufficient to reach the threshold of firing of an auditory neuron. This suggests a different mechanism for neuronal firing for onsets compared to ongoing sounds. An important aspect of this accuracy is the presence of ribbon synapses in the inner hair cells. For certain conditions, the accuracy can be as high in auditory nerve fibers as in auditory cortex. Because of the parallel processing of the output of the auditory nerve by the numerous different cell types in the cochlear nucleus, the accuracy of onset timing can be greatly enhanced over that in the auditory nerve fibers by the convergence of many of these inputs. This is exploited by the sound localization mechanisms in the brainstem. Population representation of the highly synchronous onset activity in auditory neurons results in evoked potentials that can be recorded from the scalp and play an important role in the detection of brain abnormalities in various auditory temporal processing problems. A double onset type of processing is found in echo-locating bats that show tuning in the auditory cortex to echo-delay. This delay represents the distance from the bat to the target, and is represented in a topographic map.

This chapter provides a brief introduction to a variety of neuroscience techniques other than MRI and fMRI. We first discuss standard anatomical and physiological techniques for studying neurons and their connections. We then provide brief explanations of non-MRI large-scale neuroimaging techniques used in studying humans, including EEG, MEG, CT, PET and SPECT, as well as some interventional techniques such as TMS. Because of their inferior spatial and temporal resolution, these techniques are likely to appear less often in the courtroom than is MRI and fMRI, but they still provide evidence that may be legally relevant. We conclude the chapter with a brief discussion of advances in genetics that tell us about the brain. Neurogenetics and behavioral genetics are beginning to provide interesting insights into the genetic bases of brain function and of behavioral traits.