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Biomedical subjects

G R Barnes

Publications and source records attributed to G R Barnes.

At least 19 recordsLinked to original sources
PubMed2002

Object motion perception is shaped by the motor control mechanism of ocular pursuit.

It is still a matter of debate whether the control of smooth pursuit eye movements involves an internal drive signal from object motion perception. We measured human target velocity and target position perceptions and compared them with the presumed pursuit control mechanism (model simulations). We presented normal subjects (Ns) and vestibular loss patients (Ps) with visual target motion in space. Concurrently, a visual background was presented, which was kept stationary or was moved with or against the target (five combinations). The motion stimuli consisted of smoothed ramp displacements with different dominant frequencies and peak velocities (0.05, 0.2, 0.8 Hz; 0.2-25.6 degrees /s). Subjects always pursued the target with their eyes. In a first experiment they gave verbal magnitude estimates of perceived target velocity in space and of self-motion in space. The target velocity estimates of both Ns and Ps tended to saturate at 0.8 Hz and with peak velocities >3 degrees /s. Below these ranges the velocity estimates showed a pronounced modulation in relation to the relative target-to-background motion ('background effect'; for example, 'background with'-motion decreased and 'against'-motion increased perceived target velocity). Pronounced only in Ps and not in Ns, there was an additional modulation in relation to the relative head-to-background motion, which co-varied with an illusion of self-motion in space (circular vection, CV) in Ps. In a second experiment, subjects performed retrospective reproduction of perceived target start and end positions with the same stimuli. Perceived end position was essentially veridical in both Ns and Ps (apart from a small constant offset). Reproduced start position showed an almost negligible background effect in Ns. In contrast, it showed a pronounced modulation in Ps, which again was related to CV. The results were compared with simulations of a model that we have recently presented for velocity control of eye pursuit. We found that the main features of target velocity perception (in terms of dynamics and modulation by background) closely correspond to those of the internal drive signal for target pursuit, compatible with the notion of a common source of both the perception and the drive signal. In contrast, the eye pursuit movement is almost free of the background effect. As an explanation, we postulate that the target-to-background component in the target pursuit drive signal largely neutralises the background-to-eye retinal slip signal (optokinetic reflex signal) that feeds into the eye premotor mechanism as a competitor of the target retinal slip signal. An extension of the model allowed us to simulate also the findings of the target position perception. It is assumed to be represented in a perceptual channel that is distinct from the velocity perception, building on an efference copy of the essentially accurate eye position. We hold that other visuomotor behaviour, such as target reaching with the hand, builds mainly on this target position percept and therefore is not contaminated by the background effect in the velocity percept. Generally, the coincidence of an erroneous velocity percept and an almost perfect eye pursuit movement during background motion is discussed as an instructive example of an action-perception dissociation. This dissociation cannot be taken to indicate that the two functions are internally represented in separate brain control systems, but rather reflects the intimate coupling between both functions.

Adult↗
PubMed2002

Sequence learning in human ocular smooth pursuit.

It has been established that repeated presentation of a transient target motion stimulus such as a constant-velocity ramp leads to the build up of steady state (SS), anticipatory smooth pursuit eye movements after two or three presentations. Each SS response is then composed of the anticipatory component of nonvisual origin, a visual component associated with the stimulus presentation and another nonvisual component that represents the decay of the response after extinction of the stimulus. Here we investigated the interactions that occur when each motion stimulus was itself a sequence containing more than one ramp component. Ramp components had a velocity of 15 degrees /s or 30 degrees /s to left or right and were separated by gaps of 200 ms duration. In an initial experiment, responses to 2-ramp stimuli were examined and compared with responses to the single-ramp stimuli from which they were constituted. We present evidence that the anticipatory, nonvisual components of the double-ramp response result from the linear summation of the nonvisual components of the responses to the constituent single-ramp components. In a 2nd experiment, we examined responses to a wide variety of 4-ramp sequences and again found evidence that, in the SS, the responses were formed from the linear summation of the constituent single-ramp components. Regression analysis performed on the velocity at onset of each ramp component indicated that this nonvisual part of the response was predictive of the upcoming ramp component. To confirm this, unexpected changes were introduced into single ramp components of the 4-ramp sequence after at least five prior presentations of the sequence had allowed a SS response to be established. Subjects continued to initiate a response to the modified component that was appropriate in velocity and direction for the corresponding part of the previous sequence and inappropriate for the newly modified stimulus. This preprogrammed response persisted unmodified for more than 170 ms after onset of the modified ramp component. In contrast, in the second presentation of the new sequence, the anticipatory component of the response was highly correlated with the SS response of the new sequence, but not with that of the prior sequence, showing that the preprogrammed response had been modified very rapidly. Similar behaviour was observed whichever of the 4-ramp components was modified, indicating that the velocity and direction of the anticipatory response to each component had been preprogrammed. The results suggest that velocity information related to at least four elements of a sequence can be temporarily stored and subsequently released with appropriate temporal order to form an anticipatory response throughout the whole sequence.

Brain↗
PubMed2002

Factors affecting the longevity of a short-term velocity store for predictive oculomotor tracking.

Fast (up to 30 degrees /s) anticipatory smooth pursuit eye movements can be built up with repeated transient motion stimuli. It is thought that such stimuli charge a putative internal store of velocity information that can then drive anticipatory movements in the absence of a target. The aim of this study was to investigate the longevity of this store. Previous experiments with single ramp stimuli (Wells and Barnes 1998) suggested that the store lasts for only a few seconds before decaying to a baseline level. In the current study we investigate the possibility that the store was not maximally charged by single stimuli, precipitating its decay. The magnitude of the anticipatory response was indexed by smooth eye velocity 100 ms after target onset ( V(100)). In experiment 1 the build-up of the anticipatory response was examined by presenting sets of stimuli (comprising from one to five ramps) within a tracking phase and leaving a dark period (the 'gap') of 9.6 s between successive tracking phases. Each ramp was preceded by an audio warning cue and was accompanied throughout its 480 ms duration by an audio tone. Audio cues continued during the gap to reinforce timing information. V(100) for the first and last ramps of each set increased as the number of ramps was increased from one to three but reached an asymptotic level thereafter, suggesting that the velocity store is maximally charged after three presentations. In experiment 2 the store was maximally charged by presenting five ramps in each tracking phase and its decay was examined by leaving gaps of either 7.2 s or 14.4 s between successive tracking phases. V(100) was not diminished after either gap interval. In experiment 3 the velocity store was less well consolidated during tracking phases comprising two ramps. V(100) for the first response after the gap was unaffected by the 7.2 s gap interval but was significantly reduced when the gap interval was 14.4 s. The interval between the warning cue and ramp onset strongly influenced the magnitude of the anticipatory response, the optimum level being elicited by a cue time of 600 ms. In conclusion, this study has shown that the internal velocity store can be sustained for periods as long as 14.4 s provided that it is initially charged to a sufficiently high level and that accurate external timing cues are provided. Furthermore, we provide evidence to suggest that this process may be controlled by a two-part sample and hold mechanism.

Acceleration↗
PubMed2002

Anticipatory control of hand and eye movements in humans during oculo-manual tracking.

Anticipatory activity of hand and eye has been examined during oculo-manual tracking of a constant velocity visual target with a hand cursor. Both target and cursor were presented briefly (< 480 ms), but repeatedly, at regular inter-stimulus intervals (ISI). In Expt 1, the build-up of hand and eye responses was examined for target velocities varying from 10-40 deg x s(-1) with an ISI of 2.4 s. The velocity 100 ms after target onset (i.e. prior to visual feedback) for both hand and eye (V100) progressively increased over the first four presentations but then attained a steady state (SS). SS V100 values for eye and hand increased in proportion to target velocity and were thus predictive of forthcoming movement. Hand velocity exceeded eye velocity but both exhibited similar anticipatory trajectories. In Expt 2, target velocity was constant (40 deg x s(-1)) but ISI varied from 0.48-3.74 s. Subjects made anticipatory eye movements for all ISIs but hand movements were often reactive at the longest ISI. If the target failed to appear as expected, subjects initiated predictive hand and eye responses with timing appropriate for the prevailing ISI. In Expt 3, predictive responses were compared with responses to randomised presentation. Peak hand velocity was greater in the randomised mode than in the predictive condition, whereas the converse was true for peak eye velocity. This difference is discussed in terms of the mechanisms of positional error correction in hand and eye. Results provide evidence of similar anticipatory mechanisms in hand and eye, using storage of velocity and timing to achieve rapid prediction of target motion.

Adult↗
PubMed2002

A quantitative assessment of the sensitivity of whole-head MEG to activity in the adult human cortex.

MagnetoEncephaloGraphy (MEG) relies on the detection of cortical current flow by measurement of the associated magnetic field outside the head. The amplitude of this magnetic field depends strongly on the depth of the electrical brain activity. Additionally, radially orientated sources are magnetically silent in a concentrically homogeneous volume conductor, giving rise to the anecdotal assumptions that MEG is insensitive to both deep and gyral sources. Utilising cortical surfaces extracted from Magnetic Resonance Images (MRIs) of two adult brains we constructed all possible single source elements and examined the proportion of active neocortex that is actually detectable with a whole-head MEG system. We identified those electrically active regions to which MEG is maximally sensitive by analytically computing the probability of detecting a source within a specified confidence volume. Our findings show that source depth, and not orientation, is the main factor that compromises the sensitivity of MEG to activity in the adult human cortex. There are thin strips (approximately 2 mm wide) of poor resolvability at the crests of gyri; however, these strips account for only a relatively small proportion of the cortical area and are abutted by elements with nominal tangential component yet high resolvability due to their proximity to the sensor array. Finally, we varied the extent of the patches of cortical activity, showing that small patches have a small net-current moment and are therefore less visible whereas large patches have a strong net-current moment, are generally more visible to the MEG system, yet are less appropriately modelled as single dipoles.

Adult↗
PubMed2002

The role of expectancy and volition in smooth pursuit eye movements.

The most important factor allowing the generation of pursuit eye movements prior to target onset is confidence in the likelihood of imminent target appearance. We show how these anticipatory pursuit responses are essentially ballistic motor primitives and how the signal that drives them in normally defined by stored information concerning target speed, duration and direction. But we also show how static cues may be used to grade the level of these motor primitives 'on-line'. We further demonstrate that, when concatenated, these graded motor primitives can be rapidly combined to form predictive smooth movement trajectories in response to complex multi-ramp sequences.

Cues↗
PubMed2001

The cortical deficit in humans with strabismic amblyopia.

To further our understanding of the cortical deficit in strabismic amblyopia, we measured, compared and mapped functional magnetic resonance imaging (fMRI) activation between the fixing and fellow amblyopic eyes of ten strabismic amblyopes. Of specific concern was whether the function of any visual area was spared in strabismic amblyopia, as recently suggested by both positron emission tomography (PET) and fMRI studies, and whether there was a close relationship between the fMRI response and known psychophysical deficits. To answer these questions we measured the psychophysical deficit in each subject and used stimuli whose relationship to the psychophysical deficit was known. We observed that stimuli that were well within the amblyopic passband did produce reduced fMRI activation, even in visual area V1. This suggests that V1 is anomalous in amblyopia. A similar level of reduction was observed in V2. In two subjects, we found that stimuli outside the amblyopic passband produced activation in visual area V3A. We did not find a close relationship between the fMRI response reduction in amblyopia and either of the known psychophysical deficits even though the fMRI response reduction in amblyopia did covary with stimulus spatial frequency.

Adolescent↗
PubMed2000

Ocular pursuit responses to repeated, single-cycle sinusoids reveal behavior compatible with predictive pursuit.

The link between anticipatory smooth eye movements and prediction in sinusoidal pursuit was investigated by presentation of series of identical, single-cycle, sinusoidal target motion stimuli. Stimuli occurred at randomized intervals (1.2-2.8 s) but were preceded by an audio warning cue 480 ms before each presentation. Cycle period (T) varied from 0.64 to 2.56 s and target displacement from 4 to 20 degrees in separate series. For T </= 1.28 s, responses to the first stimulus of each series exhibited a time delay across the whole cycle (mean = 121 ms for T = 0.8 s). But, in the second and subsequent (steady-state) presentations, anticipatory movements, proportional to target velocity, were made and time delay was significantly reduced (mean = 43 ms for T = 0.8 s). Steady-state time delays were comparable to those evoked during continuous sinusoidal pursuit and less than pursuit reaction time. Even when subjects did not follow the target in the first presentation, they responded to the second presentation with reduced time delay. Throughout the experiments, three types of catch trial (A-C) were introduced. In A, the target failed to appear as expected after the warning cue. Anticipatory smooth movements were initiated, reaching a peak velocity proportional to prior target velocity around 200 ms after expected target onset. In B, the target stopped midway through the cycle. Even if the target remained on and was stationary, the eye movement continued to be driven away from the stationary target with a velocity similar to that of prior responses, reaching a peak velocity that was again proportional to expected target velocity after >/=205 ms. In C, the amplitude of the single sinusoid was unexpectedly increased or decreased. When it decreased, eye velocity throughout the first half-cycle of the response was close to that executed in response to prior stimuli of higher velocity and did not return to an appropriate level for 382-549 ms. Conversely, when amplitude increased, eye velocity remained inappropriately low for the first half-cycle. Results of A and C indicate that subjects are able to use velocity information stored from prior presentations to initiate an oculomotor drive that predominates over visual feedback for the first half-cycle. Results of B indicate that the second part of the cycle is also preprogrammed because it continued despite efforts to suppress it by fixation. The results suggest that initial retinal velocity error information can be sampled, stored, and subsequently replayed as a bi-directional anticipatory pattern of movement that reduces temporal delay and could account for predictive control during sinusoidal pursuit.

Adaptation, Physiological↗
PubMed1999

Independent control of head and gaze movements during head-free pursuit in humans.

1. Head and gaze movements are usually highly co-ordinated. Here we demonstrate that under certain circumstances they can be controlled independently and we investigate the role of anticipatory activity in this process. 2. In experiment 1, subjects tracked, with head and eyes, a sinusoidally moving target. Overall, head and gaze trajectories were tightly coupled. From moment to moment, however, the trajectories could be very different and head movements were significantly more variable than gaze movements. 3. Predictive head and gaze responses can be elicited by repeated presentation of an intermittently illuminated, constant velocity target. In experiment 2 this protocol elicited a build-up of anticipatory head and gaze velocity, in opposing directions, when subjects made head movements in the opposite direction to target movement whilst maintaining gaze on target. 4. In experiment 3, head and gaze movements were completely uncoupled. Subjects followed, with head and gaze, respectively, two targets moving at different, harmonically unrelated frequencies. This was possible when both targets were visual, and also when gaze followed a visual target at one frequency whilst the head was oscillated in time with an auditory tone modulated at the second frequency. 5. We conclude that these results provide evidence of a visuomotor predictive mechanism that continuously samples visual feedback information and stores it such that it can be accessed by either the eye or the head to generate anticipatory movements. This overcomes time delays in visuomotor processing and facilitates time-sharing of motor activities, making possible the performance of two tasks simultaneously.

Acoustic Stimulation↗
PubMed1999

The remembered pursuit task: evidence for segregation of timing and velocity storage in predictive oculomotor control.

Regular, repeated presentation of identical constant-velocity target motion stimuli (ramps) appears to allow build up of an internal store, release of which can be used to generate anticipatory smooth pursuit prior to subsequent target onset. Here, we examine whether release of the anticipatory response can be controlled by timing cues unrelated to the motion stimulus itself. In experiment 1, the target moved in alternate directions and was exposed for 480 ms as it passed through centre; otherwise subjects were in darkness. Inter-stimulus interval (ISI) was either regular (3.6 s) or randomized (2.7-4.3 s). Presentations were given with or without audio cues that occurred at a constant cue time (CT) prior to target appearance. Even when ISI was randomized, cues could be used to generate anticipatory smooth pursuit. Eye velocity (V100) measured 100 ms after target onset (just prior to visual feedback influence) was greater with cues than without and decreased significantly as CT increased from 240-960 ms. In experiment 2, we assessed the effects of fixation between presentations and eccentricity of target starting position, using unidirectional ramps. The target was visible for 400 ms and started on, ended on or straddled the midline. Subjects held fixation on the midline until an audio cue signalled that preparation for ensuing target appearance could begin. There was no difference in V100 between starting positions or between presence/absence of fixation. In experiment 3, we compared the effects of using audio, visual or tactile cues. All types of cue evoked anticipatory smooth pursuit, but the response to the visual cue was significantly delayed compared with the others. However, V100 was not significantly different between cues. In all experiments, V100 was scaled in proportion to target velocity over the range 12.5-50 degrees /s, showing that this was a truly predictive response. The results provide evidence that timing and velocity storage can be independently controlled through different sensory channels and suggest that the two functions are probably carried out by separate neural mechanisms.

Acceleration↗
PubMed1999

Predictive smooth pursuit eye movements during identification of moving acuity targets.

Repetitive, brief target ramp movements every few seconds lead to anticipatory acceleration before each ramp onset and anticipatory deceleration before ramp offset. We assessed whether identifying novel changes in the pursuit target would alter this pattern of anticipatory pursuit. Without target identification (TI), anticipatory acceleration increased when intervals between ramps were regular, rather than random. It increased further when, between ramps, the target was invisible rather than stationary and visible. Anticipatory deceleration increased when the target was expected to stop rather than disappear at ramp offset. For TI trials, the pursuit target changed briefly into a Landolt C acuity target that had to be identified. Compared to no TI, anticipatory acceleration decreased when a stationary C always appeared just before ramp onset. It increased when a moving C appeared just after ramp onset, but only when the target was invisible between ramps. Anticipatory deceleration was reduced when a moving C appeared just before ramp offset, but did not increase when a stationary C appeared just after ramp offset. The changes were significant, but of small magnitude, suggesting that predictive pursuit, especially with a visible target between ramps, cannot be greatly influenced by attempts to selectively improve acuity at a particular phase of the stimulus.

Adult↗
PubMed1999

Progressive bradykinesia and hypokinesia of ocular pursuit in Parkinson's disease.

OBJECTIVES: Patients with Parkinson's disease characteristically have difficulty in sustaining repetitive motor actions. The purpose of this study was to establish if parkinsonian difficulty with sustaining repetitive limb movements also applies to smooth ocular pursuit and to identify any pursuit abnormalities characteristic of Parkinson's disease. METHODS: Ocular pursuit in seven patients with moderate to severe bradykinesia predominant Parkinson's disease was compared with seven age matched controls. Predictive and non-predictive pursuit of constant velocity target ramps were examined. Subjects pursued intermittently illuminated 40(0)/s ramps sweeping to the left or right with an exposure duration of 480 ms and average interval of 1.728 s between presentations. To examine for any temporal changes in peak eye velocity, eye displacement or anticipatory smooth pursuit the 124 s duration of each record was divided into four epochs (E1, E2, E3, E4), each lasting 31 s and containing 18 ramp stimuli. Three test conditions were examined in each subject: predictive (PRD1), non-predictive (NPD), and predictive (PRD2) in that order. RESULTS: Both patients and controls initiated appropriate anticipatory pursuit before target onset in the PRD1 and PRD2 conditions that enhanced the response compared with the NPD condition. The distinctive findings in patients with Parkinson's disease were a reduction in response magnitude compared with controls and a progressive decline of response with stimulus repetition. The deficits were explained on the basis of easy fatiguability in Parkinson's disease. CONCLUSIONS: Ocular pursuit shows distinct anticipatory movements in Parkinson's disease but peak velocity and displacement are reduced and progressively decline with repetition as found with limb movements.

Aged↗
PubMed1998

Fast, anticipatory smooth-pursuit eye movements appear to depend on a short-term store.

Anticipatory smooth pursuit before the expected appearance of a moving target can reduce the initial retinal blur caused by the 100-ms delay of visual feedback. Humans, though, can only voluntarily generate smooth velocities up to about 5 degrees/s without a moving target. However, previous experiments have shown that repetitive brief presentations of a moving target every few seconds appear to charge an internal store, the contents of which can later be released to generate higher velocity anticipatory movements. This store's longevity was assessed here by repetitively presenting a moving target for 500 ms at different known intervals up to 7.2 s. Target motion at 25 degrees/s or 50 degrees/s was tested, with presentations in alternate directions or the same direction. Anticipatory velocity, measured 100 ms after target onset, decreased with increasing interval for all target motion conditions. A decrease was still seen when accurate timing cues were given before each presentation, suggesting that the drive for anticipatory pursuit is held in a short-term store lasting a few seconds which can enhance the low velocities produced by volition alone. The results also demonstrate that high-velocity anticipatory pursuit helps to overcome the temporal delays in the system and allows target velocity to be matched at an earlier time.

Adult↗
PubMed1998

Timing variability of repetitive saccadic eye movements.

We assessed the suitability of using the Wing and Kristofferson model for timing repetitive motor responses to analyse timing variability during repetitive saccadic eye movements. The model decomposes total timing variability (TV) into a central timing component (CV) and a peripheral motor delay component (MV). Eight normal subjects made voluntary horizontal saccades, in darkness, in synchrony with a regular auditory metronome. After 20 saccades had been produced, the metronome was switched off and subjects continued responding at the same frequency until 31 further saccades had been made. Inter-saccade intervals (ISIs) from the unpaced phase were used to calculate TV, CV and MV. Three different target intervals, paced by auditory cues, were used - 496 ms, 752 ms and 1000 ms. In the paced phase, subjects' ISIs closely matched the auditory cue intervals. In the unpaced phase, subjects were clearly able to respond at three different frequencies. As predicted by the Wing and Kristofferson model, the durations of successive ISIs tended to be negatively correlated. As expected, TV and CV increased with increasing ISI. Contrary to the expectation of the model that MV would remain constant, we found that it increased with increasing interval. Our results do not conclusively demonstrate the validity of applying the Wing and Kristofferson model to the analysis of timing variability during repetitive saccadic eye movements. However, comparison with previous studies shows that, at least in normal subjects, it is equally valid to apply the model to the analysis of repetitive saccadic eye movements as it is to apply it to the analysis of data from other effectors.

Adult↗
PubMed1998

Human vestibuloocular reflex and its interactions with vision and fixation distance during linear and angular head movement.

Human vestibuloocular reflex and its interactions with vision and fixation distance during linear and angular head movement. J. Neurophysiol. 80: 2391-2404, 1998. The vestibuloocular reflex (VOR) maintains visual image stability by generating eye movements that compensate for both angular (AVOR) and linear (LVOR) head movements, typically in concert with visual following mechanisms. The VORs are generally modulated by the "context" in which head movements are made. Three contextual influences on VOR performance were studied during passive head translations and rotations over a range of frequencies (0.5-4 Hz) that emphasized shifting dynamics in the VORs and visual following, primarily smooth pursuit. First, the dynamic characteristics of head movements themselves ("stimulus context") influence the VORs. Both the AVOR and LVOR operate with high-pass characteristics relative to a head velocity input, although the cutoff frequency of the AVOR (<0.1 Hz) is far below that of the LVOR ( approximately 1 Hz), and both perform well at high frequencies that exceed, but complement, the capabilities of smooth pursuit. Second, the LVOR and AVOR are modulated by fixation distance, implemented with a signal related to binocular vergence angle ("fixation context"). The effect was quantified by analyzing the response during each trial as a linear relationship between LVOR sensitivity (in deg/cm), or AVOR gain, and vergence (in m-1) to yield a slope (vergence influence) and an intercept (response at 0 vergence). Fixation distance (vergence) was modulated by presenting targets at different distances. The response slope rises with increasing frequency, but much more so for the LVOR than the AVOR, and reflects a positive relationship for all but the lowest stimulus frequencies in the AVOR. A third influence is the context of real and imagined targets on the VORs ("visual context"). This was studied in two ways-when targets were either earth-fixed to allow visual enhancement of the VOR or head-fixed to permit visual suppression. The VORs were assessed by extinguishing targets for brief periods while subjects continued to "fixate" them in darkness. The influences of real and imagined targets were most robust at lower frequencies, declining as stimulus frequency increased. The effects were nearly gone at 4 Hz. These properties were equivalent for the LVOR and AVOR and imply that the influences of real and imagined targets on the VORs generally follow low-pass and pursuit-like dynamics. The influence of imagined targets accounts for roughly one-third of the influence of real targets on the VORs at 0.5 Hz.

Adult↗
PubMed1996

Abnormalities of smooth eye and head movement control in Parkinson's disease.

The control of horizontal head and eye movements was examined in 13 nondemented patients with Parkinson's disease (PD) of mild to moderate severity. During pursuit of single-frequency sine waves, smooth component eye velocity was lower in the PD group at frequencies of 1.2 Hz and above; but the differences in overall eye displacement were even greater, indicating an impaired ability to generate catch-up saccades at high frequencies. A corresponding deficit in saccadic performance was observed during a high-frequency saccadic tracking task where predictive saccades of reduced gain and variable timing were generated. During pursuit of pseudo-random target motion with varying degrees of predictability, small differences in smooth component eye velocity were observed, but prediction was otherwise well preserved in the patient group. Vestibulo-ocular reflex (VOR) suppression was also normal during head-free pursuit. No major improvement in smooth pursuit gain could be attributed to drug treatment, based on a comparison of patient results before and after administration of levodopa.

Adult↗
PubMed1996

Assessment of the humane aspects of electric lancing of whales by measurement of current densities in the brain and heart of dead animals.

The potential physiological effects of the electric lance are assessed, as used in Japanese whaling operations. Current densities are measured in the brains and hearts of six whales to which a controlled current of 5 A is applied by two electrodes inserted at various sites in the carcasses. The whales vary in size from 1.8 m (22 kg) to 16 m (40 t). The minimum current density in the brain necessary to cause depolarisation of neurones is estimated to be 10 mA cm-2 and to cause ventricular fibrillation is estimated to be 0.5 mA cm-2. No current densities exceeding 4.8 mA cm-2 are recorded in the brain. Very few recordings of current density from the heart are above 0.5 mA cm-2, and they occur only when electrodes are in optimal positions. When electrodes are placed as in whaling operations, no whale over 3 m in length would receive current densities in the heart or brain sufficient to cause permanent dysfunction. It is concluded that electric lancing is ineffective as a secondary method of killing whales and that the current densities recorded could cause pain and suffering to an already distressed animal.

Animals↗