Large-field Responses Research Articles

Assessment of digital light processing (DLP) projector stimulators for visual electrophysiology

IntroductionVisual electrophysiology tests require the use of precise and calibrated visual display units (VDUs). Existing VDUs for presenting structured stimuli are now mostly obsolete, with modern solutions limited or unsuitable for clinical testing. Digital light processing (DLP) laser projectors have recently become commercially available and this study aimed to assess their suitability as VDUs for visual electrophysiology testing.MethodsThis study consisted of two sections. The first was a photometric study of two DLP laser projectors (Viewsonic LS831WU and HiSense 100L5FTUK) to assess luminance, contrast, spectral and temporal characteristics of the stimulus. The second was a physiological study comparing pattern electroretinograms (PERG) and visual evoked potentials (PVEPs) amplitudes and peak-times recorded using a DLP laser projector, photometrically and spatially matched to existing plasma VDUs at our institution (Pioneer Electronics Corporation, PDP422MXE).ResultsThe Viewsonic DLP laser projector was capable of high luminance levels (0–587.5 cd/m2) whilst maintaining contrast above 93%. The temporal properties showed fast rise and fall times of 0.5–1 ms and 0.5–1 ms, respectively, without any transient luminance change with reversals. The device required a warm-up time of at least 2 min until reaching near maximal luminance. The second (Hisense) device was observed to have a detrimental input lag jitter so was not used for any further analysis. PERGs and PVEPs showed high agreement and correlation (r = 0.766–0.905) between the Viewsonic DLP device and existing plasma VDUs. No significant differences were observed for P50 and P100 peak-time (p = > 0.05), however P50, N95 and P100 amplitudes were all significantly larger for the DLP device (p = < 0.05).DiscussionThe DLP laser projector tested in this study is a viable and practical replacement VDU for clinical electrophysiology tests of vision. The device is easily capable of meeting ISCEV standards, and showed PERG and PVEP amplitudes larger than existing systems despite photometric and spatial matching. The DLP laser projectors are capable of very large field sizes so are beneficial for paediatric testing or those wishing to examine large field responses. Importantly, it was observed that some devices may suffer input lag jitter, therefore, individual calibration and assessment of DLP projection systems is an important consideration before clinical implementation.

Ferroelectric, ferroelastic, piezoelectric, and dielectric properties of lead zirconate titanate from –150 °C to 350 °C

The ferroelectric, ferroelastic, piezoelectric, and dielectric properties of co-doped, soft-type Pb(Zr,Ti)O3 were measured from −150°C to 350°C, highlighting the importance of temperature and defects on the electromechanical response. Small signal piezoelectric measurements revealed a linear increase with increasing temperatures below 0°C, followed by a maximum at approximately 50°C. The low temperature properties correspond well to observed changes in the large-field response during the application of an external electrical and mechanical field. The results illustrate the importance of understanding phase boundary effects in order to determine a useable temperature range and to tailor future lead free piezoelectric materials for cryogenic electromechanical applications.

Genetic dissection of optomotor behavior in Drosophila melanogaster. Studies on wild-type and the mutant optomotor-blindH31.

In stationary flight Drosophila melanogaster produces yaw torque in response to visual movement stimuli. The residual optomotor yaw torque response of the mutant optomotor-blindH31 (omb), which lacks the horizontal (HS) and vertical (VS) giant fibers in the lobula plate, differs from that of wild-type in several aspects: it is restricted to the frontal visual field, it is only elicited by front-to-back motion and appears to be mediated by a different set of elementary movement detectors (EMDs). Using a single black stripe as motion stimulus the torque response is, even in wild-type flies, dominated by the frontal visual field and by front-to-back motion. We thus propose that Drosophila's optomotor yaw control is organized as two partially parallel subunits. The component still displayed by omb is called "object response"; the component missing in the mutant (which is presumably mediated by the giant HS-cells in the wild-type) is called "large field response". Several properties of the object response are described.

Stimulus dependent colour specificity of monkey lateral geniculate neurones

From six flaxedilized rhesus monkeys neuronal activity of 75 cells in the dorsal, and 45 cells in the ventral layers of the lateral geniculate body was recorded. Responses to large fields switched on and off, to moving slits, and to moving spots were obtained for several wavelengths. In the dorsal layers, colour selectivity was strong for large field stimuli but weak for moving spots. Residual colour selectivity for spots was more evident for smaller eccentricities. In comparison, ventral layer cells were less colour selective for all stimuli used. Large field responses were weak, they often consisted of a sequence of excitation and inhibition. The subdivision of the dorsal cells into different colour opponency types based on large field responses is compared to the subdivision based on centre and surround functions. Results are compared to colour responses in retina and visual cortex, and the tonic and phasic cell type subdivision is discussed.

Development and application of white-noise modeling techniques for studies of insect visual nervous system.

The nonlinear system identification technique through white-noise stimulation is extended to multi-input, -output systems with consideration given to applications in the functional study of the nervous system. The applicability of the method is discussed in general and in particular for the motion detection neuronal system of the fly. Two series of experiments are performed; one with moving striped-pattern stimuli and the other with spot stimuli of fluctuating intensity. In both cases nonlinear dynamic models are derived which describe the system with considerable accuracy over the frequency range of 0.2–50 Hz and a dynamic amplitude range of about 40-1. These models are able to predict accurately all the discrete experiments so far performed on this system for which the models are applicable. The differences in dynamic characteristics between the corresponding system of the Musca and Phoenicia families of flies are minor except for a difference in latencies and if the difference in geometry of their faceted eyes is taken into account. The large field response of the motion detection unit is a linear weighted summation of all the smaller field highly nonlinear subsystems of which the large field is comprised.

Field potentials in rat hippocampus: Monosynaptic nature and heterosynaptic post-tetanic potentiation

Subicular, commisural, and fornical stimulation evoked large field responses in the dentate gyrus and dorsal hippocampus of rats. Hippocampal responses were negative above and positive below the upper third of apical dendrites in CA1, CA2, and CA3; the application of a pressing foot on the alveus resulted in a distortion of this polarity pattern. Since a compound action potential was found in the fornix during the rising phase of hippocampal field responses, it was concluded that the latter correlated with excitation of pyramidal cells. The following frequency of dentate and hippocampal potentials was high (up to 125/sec) and similar for both; thus, it was concluded that both were monosynaptic responses. On the basis of excluding several impossible mechanisms, hippocampal field potentials were attributed to a flow of cations, through the extracellular clefts, from the stratum pyramidale down to the stratum radiale. Hippocampal- and dentate-evoked potentials suffered post-tetanic potentiation; in the case of hippocampal responses, this was both homo- and heterosynaptic. The possible relevance of the latter to mechanisms of learning, and the possible genesis of both by (K +) 0 accumulation were discussed.