RESUMO
Visual display was used by Stäb and Ilg to examine the abilities of video-game players and non-players to determine simple mathematical abilities.
Assuntos
Conceitos Matemáticos , Jogos de Vídeo , Adolescente , Cognição/fisiologia , Estudos Transversais , Feminino , Humanos , Modelos Lineares , Masculino , Fatores de Tempo , Adulto JovemRESUMO
By 2050, the global population of people aged 65 years or older will triple. While this is accompanied with an increasing burden of age-associated diseases, it also emphasizes the need to understand the effects of healthy aging on cognitive processes. One such effect is a general slowing of processing speed, which is well documented in many domains. The execution of anti-saccades depends on a well-established brain-wide network ranging from various cortical areas and basal ganglia through the superior colliculus down to the brainstem saccade generators. To clarify the consequences of healthy aging as well as gender on the execution of reflexive and voluntary saccades, we measured a large sample of healthy, non-demented individuals (n = 731, aged 51-84 years) in the anti-saccade task. Age affected various aspects of saccade performance: The number of valid trials decreased with age. Error rate, saccadic reaction times (SRTs), and variability in saccade accuracy increased with age, whereas anti-saccade costs, accuracy, and peak velocity of anti-saccades and direction errors were not affected by age. Gender affected SRTs independent of age and saccade type with male participants having overall shorter SRTs. Our rigid and solid statistical testing using linear mixed-effect models provide evidence for a uniform slowing of processing speed independent of the actually performed eye movement. Our data do not support the assumption of a specific deterioration of frontal lobe functions with aging.
Assuntos
Envelhecimento Saudável , Movimentos Sacádicos , Envelhecimento , Humanos , Masculino , Tempo de Reação , Colículos SuperioresRESUMO
BACKGROUND: Falls frequency increases with age and particularly in neurogeriatric cohorts. The interplay between eye movements and locomotion may contribute substantially to the occurrence of falls, but is hardly investigated. This paper provides an overview of current approaches to simultaneously measure eye and body movements, particularly for analyzing the association of vestibulo-ocular reflex (VOR) suppression, postural deficits and falls in neurogeriatric risk cohorts. Moreover, VOR suppression is measured during head-fixed target presentation and during gaze shifting while postural control is challenged. Using these approaches, we aim at identifying quantitative parameters of eye-head-coordination during postural balance and gait, as indicators of fall risk. METHODS/DESIGN: Patients with Progressive Supranuclear Palsy (PSP) or Parkinson's disease (PD), age- and sex-matched healthy older adults, and a cohort of young healthy adults will be recruited. Baseline assessment will include a detailed clinical assessment, covering medical history, neurological examination, disease specific clinical rating scales, falls-related self-efficacy, activities of daily living, neuro-psychological screening, assessment of mobility function and a questionnaire for retrospective falls. Moreover, participants will simultaneously perform eye and head movements (fixating a head-fixed target vs. shifting gaze to light emitting diodes in order to quantify vestibulo-ocular reflex suppression ability) under different conditions (sitting, standing, or walking). An eye/head tracker synchronized with a 3-D motion analysis system will be used to quantify parameters related to eye-head-coordination, postural balance, and gait. Established outcome parameters related to VOR suppression ability (e.g., gain, saccadic reaction time, frequency of saccades) and motor related fall risk (e.g., step-time variability, postural sway) will be calculated. Falls will be assessed prospectively over 12 months via protocols and monthly telephone interviews. DISCUSSION: This study protocol describes an experimental setup allowing the analysis of simultaneously assessed eye, head and body movements. Results will improve our understanding of the influence of the interplay between eye, head and body movements on falls in geriatric high-risk cohorts.
Assuntos
Acidentes por Quedas , Envelhecimento/fisiologia , Transtornos Neurológicos da Marcha/fisiopatologia , Doença de Parkinson/fisiopatologia , Equilíbrio Postural/fisiologia , Reflexo Vestíbulo-Ocular/fisiologia , Paralisia Supranuclear Progressiva/fisiopatologia , Adulto , Idoso , Estudos de Casos e Controles , Estudos Transversais , Movimentos Oculares/fisiologia , Feminino , Seguimentos , Movimentos da Cabeça/fisiologia , Humanos , Masculino , Pessoa de Meia-Idade , Estudos ProspectivosRESUMO
Electrophysiological and micro-stimulation studies in non-human animal species indicated that the superior colliculus (SC) plays a role in the control of upper limb movements. In our previous work we found reach-related signals in the deep superior colliculus in humans. Here we show that also signals in more dorsal locations are correlated with the execution of arm movements. We instructed healthy participants to reach for visual targets either presented in the left or in the right visual hemifield during an fMRI measurement. Visual stimulation was dissociated from movement execution using a pro- and anti-reaching task. Thereby, we successfully differentiated between signals at these locations induced by the visual input of target presentations on the one hand and by the execution of arm movements on the other hand. Extending our previous report, the results of this study are in good agreement with the observed anatomical distribution of reach-related neurons in macaques. Obviously, reach-related signals can be found across a considerable depth range also in humans.
Assuntos
Mapeamento Encefálico , Atividade Motora/fisiologia , Desempenho Psicomotor/fisiologia , Colículos Superiores/fisiologia , Adulto , Braço/fisiologia , Feminino , Lateralidade Funcional , Humanos , Processamento de Imagem Assistida por Computador , Imageamento por Ressonância Magnética , Masculino , Estimulação Luminosa , Adulto JovemRESUMO
The motion areas of posterior parietal cortex extract information on visual motion for perception as well as for the guidance of movement. It is usually assumed that neurons in posterior parietal cortex represent visual motion relative to the retina. Current models describing action guided by moving objects work successfully based on this assumption. However, here we show that the pursuit-related responses of a distinct group of neurons in area MST of monkeys are at odds with this view. Rather than signaling object image motion on the retina, they represent object motion in world-centered coordinates. This representation may simplify the coordination of object-directed action and ego motion-invariant visual perception.
Assuntos
Percepção de Movimento/fisiologia , Neurônios/fisiologia , Lobo Parietal/fisiologia , Acompanhamento Ocular Uniforme/fisiologia , Potenciais de Ação/fisiologia , Animais , Fixação Ocular/fisiologia , Macaca mulatta , Masculino , Orientação/fisiologia , Lobo Parietal/citologia , Estimulação Luminosa , Retina/fisiologia , Vias Visuais/fisiologiaRESUMO
It is well established that elementary motion detectors are only able to code for the movement of a contour perpendicular to its orientation. This shortcoming explains why the initial direction of smooth-pursuit eye movements is directed orthogonal to the orientation of a moving contour independent of its veridical direction of motion. Here, we replicated this finding and asked whether this directional error can be reduced by subjects' prediction of upcoming target moving direction and whether this directional error also occurs during tracking of an illusory contour. Our results show that prediction did not abolish the directional error, it was only slightly reduced. On the other hand, the directional error was considerably diminished during pursuit initiation towards illusory contours and most likely reflected the amount of real stimulation defining the specific illusory contour. We conclude that pursuit initiation is driven by raw retinal image motion signals, which are not yet processed for figure completion.
Assuntos
Percepção de Forma/fisiologia , Ilusões Ópticas/fisiologia , Acompanhamento Ocular Uniforme/fisiologia , Adulto , Feminino , Humanos , Masculino , Fechamento Perceptivo , Estimulação Luminosa/métodos , Psicofísica , Tempo de Reação/fisiologiaRESUMO
A fundamental problem in the generation of goal-directed behaviour is caused by the inevitable latency of biological sensory systems. Behaviour which is fully synchronised with the triggering sensory event can only be executed if the occurrence of this event can be predicted based on prior information. Smooth-pursuit eye movements are a classical and well-established example of goal-directed behaviour. The execution of these eye movements is thought to be very closely linked to the processing of visual motion signals. Here, we show that healthy human subjects as well as trained rhesus monkeys are able to initiate smooth-pursuit eye movements in anticipation of a moving target. These anticipatory pursuit eye movements are scaled to the velocity of the expected target. Furthermore, we can exclude the possibility that anticipatory pursuit is simply an after-pursuit of the previous trial. Visually-guided pursuit is only marginally affected by the presence of a structured background. However, the presence of a structured background severely impedes the ability to perform anticipatory pursuit. More generally, our data provide additional evidence that the cognitive oculomotor repertoires of human and monkeys are similar, at least with respect of smooth-pursuit in the prediction of an appearing target.
Assuntos
Intenção , Percepção de Movimento/fisiologia , Desempenho Psicomotor/fisiologia , Acompanhamento Ocular Uniforme/fisiologia , Adulto , Animais , Feminino , Haplorrinos , Humanos , Macaca mulatta , Masculino , Estimulação Luminosa/métodos , Tempo de Reação/fisiologia , Especificidade da EspécieRESUMO
Smooth pursuit eye movements are performed in order to prevent retinal image blur of a moving object. Rhesus monkeys are able to perform smooth pursuit eye movements quite similar as humans, even if the pursuit target does not consist in a simple moving dot. Therefore, the study of the neuronal responses as well as the consequences of micro-stimulation and lesions in trained monkeys performing smooth pursuit is a powerful approach to understand the human pursuit system. The processing of visual motion is achieved in the primary visual cortex and the middle temporal area. Further processing including the combination of retinal image motion signals with extra-retinal signals such as the ongoing eye and head movement occurs in subsequent cortical areas as the medial superior temporal area, the ventral intraparietal area and the frontal and supplementary eye field. The frontal eye field especially contributes anticipatory signals which have a substantial influence on the execution of smooth pursuit. All these cortical areas send information to the pontine nuclei, which in turn provide the input to the cerebellum. The cerebellum contains two pursuit representations: in the paraflocculus/flocculus region and in the posterior vermis. While the first representation is most likely involved in the coordination of pursuit and the vestibular-ocular reflex, the latter is involved in the precise adjustments of the eye movements such as adaptation of pursuit initiation. The output of the cerebellum is directed to the moto-neurons of the extra-ocular muscles in the brainstem.
Assuntos
Encéfalo/fisiologia , Macaca mulatta/fisiologia , Percepção de Movimento/fisiologia , Percepção Visual/fisiologia , Animais , Encéfalo/anatomia & histologia , Macaca mulatta/anatomia & histologia , Neurônios/citologia , Neurônios/fisiologia , Reflexo Vestíbulo-Ocular/fisiologia , Córtex Visual/anatomia & histologia , Córtex Visual/fisiologia , Campos Visuais/fisiologiaRESUMO
Smooth-pursuit eye movements are used to stabilize the image of a moving object of interest on the fovea, thus guaranteeing its high-acuity scrutiny. Such movements are based on a phylogenetically recent cerebro-ponto-cerebellar pathway that has evolved in parallel with foveal vision. Recent work has shown that a network of several cerebrocortical areas directs attention to objects of interest moving in three dimensions and reconstructs the trajectory of the target in extrapersonal space, thereby integrating various sources of multimodal sensory and efference copy information, as well as cognitive influences such as prediction. This cortical network is the starting point of a set of parallel cerebrofugal projections that use different parts of the dorsal pontine nuclei and the neighboring rostral nucleus reticularis tegmenti pontis as intermediate stations to feed two areas of the cerebellum, the flocculus-paraflocculus and the posterior vermis, which make mainly complementary contributions to the control of smooth pursuit.
Assuntos
Acompanhamento Ocular Uniforme/fisiologia , Animais , Cerebelo/fisiologia , Córtex Cerebral/fisiologia , Vias Eferentes/fisiologia , Humanos , Aprendizagem/fisiologia , Ponte/fisiologiaRESUMO
When our eyes track objects that are moving in a richly structured environment, the retinal image of the stationary visual scene inevitably moves over the retina in a direction opposite to the eye movement. Such self-motion-induced global retinal slip usually provides an ideal stimulus for the optokinetic reflex. This reflex operates to compensate for global image flow. However, during smooth pursuit eye movements it must be shut down so that the reflex does not counteract the voluntary pursuit of moving targets. Here, we asked if retinal information is sufficient for this cancellation of the optokinetic reflex during smooth pursuit eye movements. In a series of experiments, we show that neither the eye movement-induced retinal image motion per se nor the relative motion between the pursuit target and the background are sufficient for suppression of optokinesis. We, therefore, conclude that extra-retinal information about smooth pursuit eye movements is required for the cancellation of the optokinetic reflex.
Assuntos
Percepção de Movimento/fisiologia , Acompanhamento Ocular Uniforme/fisiologia , Piscadela/fisiologia , Fixação Ocular/fisiologia , Humanos , Estimulação Luminosa/métodos , Desempenho Psicomotor/fisiologia , Psicofísica , Reflexo/fisiologia , Retina/fisiologiaRESUMO
Video games have become both a widespread leisure activity and a substantial field of research. In a variety of tasks, video game players (VGPs) perform better than non-video game players (NVGPs). This difference is most likely explained by an alteration of the basic mechanisms underlying visuospatial attention. More specifically, the present study hypothesizes that VGPs are able to shift attention faster than NVGPs. Such alterations in attention cannot be disentangled from changes in stimulus-response mappings in reaction time based measurements. Therefore, we used a spatial cueing task with varying cue lead times (CLTs) to investigate the speed of covert attention shifts of 98 male participants divided into 36 NVGPs and 62 VGPs based on their weekly gaming time. VGPs exhibited higher peak and mean performance than NVGPs. However, we did not find any differences in the speed of covert attention shifts as measured by the CLT needed to achieve peak performance. Thus, our results clearly rule out faster stimulus-response mappings as an explanation for the higher performance of VGPs in line with previous studies. More importantly, our data do not support the notion of faster attention shifts in VGPs as another possible explanation.
Assuntos
Atenção , Percepção de Cores , Sinais (Psicologia) , Reconhecimento Visual de Modelos , Desempenho Psicomotor , Tempo de Reação , Aprendizagem Espacial , Jogos de Vídeo/psicologia , Adolescente , Adulto , Feminino , Humanos , MasculinoRESUMO
If an object of great interest moves in our environment, we are able to elicit smooth pursuit eye movements that keep the image of the moving object stationary on our fovea. The processing of visual motion underlying the execution of smooth pursuit eye movements is very similar to the processing underlying the perception of visual motion. During initiation of smooth pursuit, an averaging across all available motion information occurs. Cognitive factors including attention, prediction and learning are able to influence the execution of smooth pursuit. The pursuit target trajectory in space is represented in the discharge rates of neurons in the posterior parietal cortex of rhesus monkeys.
Assuntos
Movimentos Oculares/fisiologia , Acompanhamento Ocular Uniforme/fisiologia , Visão Ocular/fisiologia , Animais , Atenção/fisiologia , Sinais (Psicologia) , Humanos , Aprendizagem , Percepção de Movimento/fisiologia , Retina/fisiologiaRESUMO
Here, I report that rhesus monkeys are able to generate anticipatory smooth pursuit eye movements in the transient absence of a moving target, if this target moves periodically. The eye velocity before target reappearance was significantly larger if the target trajectory was predictable compared with the control condition consisting of unpredictable target trajectory. Parallel to the registration of the eye movements, single-unit activity was recorded from neurons in the middle superior temporal (MST) area of the two monkeys. The neuronal activity of visual-tracking neurons resembled the observed eye movements, i.e. these neurons increased their activity earlier if the movement of the target was predictable compared with the unpredictable control. These results provide further evidence for the existence of extra-retinal signals in the activity of visual-tracking neurons located in area MST.
Assuntos
Potenciais de Ação/fisiologia , Neurônios/fisiologia , Estimulação Luminosa/métodos , Acompanhamento Ocular Uniforme/fisiologia , Lobo Temporal/fisiologia , Animais , Macaca mulatta , Masculino , Córtex Visual/fisiologia , Vias Visuais/fisiologiaRESUMO
Video game play has become a common leisure activity all around the world. To reveal possible effects of playing video games, we measured saccades elicited by video game players (VGPs) and non-players (NVGPs) in two oculomotor tasks. First, our subjects performed a double-step task. Second, we asked our subjects to move their gaze opposite to the appearance of a visual target, i.e. to perform anti-saccades. As expected on the basis of previous studies, VGPs had significantly shorter saccadic reaction times (SRTs) than NVGPs for all saccade types. However, the error rates in the anti-saccade task did not reveal any significant differences. In fact, the error rates of VGPs were actually slightly lower compared to NVGPs (34% versus 40%, respectively). In addition, VGPs showed significantly higher saccadic peak velocities in every saccade type compared to NVGP. Our results suggest that faster SRTs in VGPs were associated with a more efficient motor drive for saccades. Taken together, our results are in excellent agreement with earlier reports of beneficial video game effects through the general reduction in SRTs. Our data clearly provides additional experimental evidence for an higher efficiency of the VGPs on the one hand and refutes the notion of a reduced impulse control in VGPs on the other.
Assuntos
Atenção/fisiologia , Desempenho Psicomotor/fisiologia , Movimentos Sacádicos/fisiologia , Jogos de Vídeo , Adolescente , Adulto , Análise de Variância , Feminino , Humanos , Masculino , Estimulação Luminosa/métodos , Tempo de Reação/fisiologia , Adulto JovemRESUMO
Eye movements create an ever-changing image of the world on the retina. In particular, frequent saccades call for a compensatory mechanism to transform the changing visual information into a stable percept. To this end, the brain presumably uses internal copies of motor commands. Electrophysiological recordings of visual neurons in the primate lateral intraparietal cortex, the frontal eye fields, and the superior colliculus suggest that the receptive fields (RFs) of special neurons shift towards their post-saccadic positions before the onset of a saccade. However, the perceptual consequences of these shifts remain controversial. We wanted to test in humans whether a remapping of motion adaptation occurs in visual perception.The motion aftereffect (MAE) occurs after viewing of a moving stimulus as an apparent movement to the opposite direction. We designed a saccade paradigm suitable for revealing pre-saccadic remapping of the MAE. Indeed, a transfer of motion adaptation from pre-saccadic to post-saccadic position could be observed when subjects prepared saccades. In the remapping condition, the strength of the MAE was comparable to the effect measured in a control condition (33±7% vs. 27±4%). Contrary, after a saccade or without saccade planning, the MAE was weak or absent when adaptation and test stimulus were located at different retinal locations, i.e. the effect was clearly retinotopic. Regarding visual cognition, our study reveals for the first time predictive remapping of the MAE but no spatiotopic transfer across saccades. Since the cortical sites involved in motion adaptation in primates are most likely the primary visual cortex and the middle temporal area (MT/V5) corresponding to human MT, our results suggest that pre-saccadic remapping extends to these areas, which have been associated with strict retinotopy and therefore with classical RF organization. The pre-saccadic transfer of visual features demonstrated here may be a crucial determinant for a stable percept despite saccades.
Assuntos
Percepção de Movimento/fisiologia , Movimentos Sacádicos/fisiologia , Percepção Visual/fisiologia , Adulto , Animais , Movimentos Oculares/fisiologia , Feminino , Humanos , Masculino , Primatas , Adulto JovemRESUMO
Saccades are very rapid eye movements in between two phases of fixation, which offer a precise measure of behaviour for the direction of the spotlight of attention. The onset of global motion is known to attract our attention reflexively. We asked whether brief global motion stimuli are able to modify the execution of saccades. When participants performed visually guided saccades towards a target presented in front of a structured background, saccade latency was 174 ms on average and correctness of saccades was 100%. If the presentation of the target occurred at the same time as the onset of a brief global motion signal, then the saccade latency increased dramatically to 243 ms with a slight decrease in correctness to 89%. However, if the motion stimulus preceded the presentation of the target, then the latency decreased to 114 ms while the correctness dropped close to chance levels (62%).
Assuntos
Percepção de Movimento/fisiologia , Movimentos Sacádicos/fisiologia , Adulto , Humanos , Pessoa de Meia-Idade , Movimento (Física) , Estimulação LuminosaRESUMO
What is the main purpose of visual motion processing? One very important aspect of motion processing is definitively the generation of smooth pursuit eye movements. These eye movements avoid motion blur of moving objects which would obstruct the analysis of the objects' visual details. However, these eye movements can only be executed if there is a moving target. So there is a very close and inseparable relationship between smooth pursuit and motion processing. The hub for visual motion processing is situated in the middle temporal (MT) and medial superior temporal (MST) area. Despite the undoubted importance of these areas for the generation of smooth pursuit or goal-directed behavior in general, it is important to keep in mind that motion processing in addition serves perceptual purposes such as object recognition, structure-from-motion detection, scene segmentation, self-motion estimation and depth perception. This review focuses at the beginning on pursuit-related activity recorded from MT and MST, subsequently extends the view to goal-directed hand movements, and finally addresses the possible contributions of these areas to motion perception.
Assuntos
Percepção de Movimento/fisiologia , Acompanhamento Ocular Uniforme/fisiologia , Animais , Mapeamento Encefálico , Movimentos da Cabeça/fisiologia , Macaca mulatta , Neurônios/fisiologia , Lobo Temporal/fisiologiaRESUMO
The contributions of the middle superior temporal area (MST) in the posterior parietal cortex of rhesus monkeys to the generation of smooth-pursuit eye movements as well as the contributions to motion perception are well established. Here, we present the first experimental evidence that this area also contributes to the generation of goal-directed hand movements toward a moving target. This evidence is based on the outcome of intracortical microstimulation experiments and transient lesions by small injections of muscimol at identified sites within the lateral part of area MST (MST-l). When microstimulation was applied during the execution of smooth-pursuit eye movements, postsaccadic eye velocity in the direction of the preferred direction of the stimulated site increased significantly (in 93 of 136 sites tested). When microstimulation was applied during a hand movement trial, the hand movement was displaced significantly in the same direction (in 28 of 39 sites tested). When we lesioned area MST-l transiently by injections of muscimol, steady-state eye velocity was exclusively reduced for ipsiversive smooth-pursuit eye movements. In contrast, hand movements were displaced toward the contralateral side, irrespective of the direction of the moving target. Our results provide evidence that area MST-l is involved in the processing of moving targets and plays a role in the execution of smooth-pursuit eye movements as well as visually guided hand movements.
Assuntos
Mãos/fisiologia , Percepção de Movimento/fisiologia , Orientação/fisiologia , Desempenho Psicomotor/fisiologia , Acompanhamento Ocular Uniforme/fisiologia , Lobo Temporal/fisiologia , Córtex Visual/fisiologia , Potenciais de Ação/efeitos dos fármacos , Potenciais de Ação/fisiologia , Animais , Atenção/fisiologia , Estimulação Elétrica , Agonistas GABAérgicos/farmacologia , Macaca mulatta , Masculino , Percepção de Movimento/efeitos dos fármacos , Movimento/efeitos dos fármacos , Movimento/fisiologia , Muscimol/farmacologia , Neurônios/efeitos dos fármacos , Neurônios/fisiologia , Testes Neuropsicológicos , Orientação/efeitos dos fármacos , Estimulação Luminosa , Desempenho Psicomotor/efeitos dos fármacos , Acompanhamento Ocular Uniforme/efeitos dos fármacos , Percepção Espacial/efeitos dos fármacos , Percepção Espacial/fisiologia , Lobo Temporal/efeitos dos fármacos , Córtex Visual/efeitos dos fármacos , Vias Visuais/efeitos dos fármacosRESUMO
Saccades are very fast, ballistic movements, which move the eyes from one target to another. Here, we show that the latency, precision and kinematics of saccades directed toward a target presented on a dark homogeneous background do not differ from the parameters of saccades directed toward a target presented on a structured background. However, if the visual background changed either its luminance or orientation simultaneously with the presentation of the saccade target, a significant increase in saccade latency was observed. The saccade kinematics as well as saccade precision, however, was not affected. Likewise, additional auditory stimulation applied simultaneously with the presentation of the target did not increase saccade latency. The increase in saccade latency and the maintenance of saccade kinematics indicate a sensory channel overload caused by the change in background. As a consequence, execution of the saccade was delayed until the computational resources to program the eye movement were available again.
Assuntos
Sensibilidades de Contraste/fisiologia , Orientação , Tempo de Reação/fisiologia , Movimentos Sacádicos/fisiologia , Estimulação Acústica/métodos , Análise de Variância , Fenômenos Biomecânicos , Fixação Ocular , Humanos , Estimulação Luminosa/métodosRESUMO
For the detection of a moving object, segregating the object from the background is a necessary first step. This segregation can be achieved by detection of differences in the spatial, temporal and spatio-temporal properties of the object and background. Here we investigate how flicker influences the perception of a moving object in man and monkey, and we examine the neuronal responses in extrastriate medial temporal and medial superior temporal areas (MT and MST) of two rhesus monkeys. The performance of humans and monkeys in a direction discrimination task was impaired in the presence of flicker in the background compared to the static background condition. A similar effect was found in recordings from 155 single units in areas MT and MST during the discrimination task. The discriminability (d') of the neuronal responses in preferred and nonpreferred directions was reduced by 33% on average in the presence of a flicker background compared to the static background. This reduction in discriminability was not caused by differences in variance of the neuronal activity for the two background conditions, but was due to a reduction of the difference between the activities in preferred and nonpreferred direction. This reduction in directional selectivity could be traced back to two different mechanisms: in 32 out of 155 neurons (21%), the decrease resulted from an increase in the response to the stimulus moving in the nonpreferred direction; in 62 out of 155 neurons (40%), the reduction in directional selectivity was due to a decrease in the response to the preferred direction. These results give deeper insights into how moving stimuli are processed in the presence of background flicker as present in natural visual scenes.