Analytical Evaluation of Signal-to-Noise Ratios for Avalanche- and Single-Photon Avalanche Diodes.

Performance of systems for optical detection depends on the choice of the right detector for the right application. Designers of optical systems for ranging applications can choose from a variety of highly sensitive photodetectors, of which the two most prominent ones are linear mode avalanche photodiodes (LM-APDs or APDs) and Geiger-mode APDs or single-photon avalanche diodes (SPADs). Both achieve high responsivity and fast optical response, while maintaining low noise characteristics, which is crucial in low-light applications such as fluorescence lifetime measurements or high intensity measurements, for example, Light Detection and Ranging (LiDAR), in outdoor scenarios. The signal-to-noise ratio (SNR) of detectors is used as an analytical, scenario-dependent tool to simplify detector choice for optical system designers depending on technologically achievable photodiode parameters. In this article, analytical methods are used to obtain a universal SNR comparison of APDs and SPADs for the first time. Different signal and ambient light power levels are evaluated. The low noise characteristic of a typical SPAD leads to high SNR in scenarios with overall low signal power, but high background illumination can saturate the detector. LM-APDs achieve higher SNR in systems with higher signal and noise power but compromise signals with low power because of the noise characteristic of the diode and its readout electronics. Besides pure differentiation of signal levels without time information, ranging performance in LiDAR with time-dependent signals is discussed for a reference distance of 100 m. This evaluation should support LiDAR system designers in choosing a matching photodiode and allows for further discussion regarding future technological development and multi pixel detector designs in a common framework.

Contribution of the Cerebellum in Cue-Dependent Force Changes During an Isometric Precision Grip Task.

The "raspberry task" represents a precision grip task that requires continuous adjustment of grip forces and pull forces. During this task, subjects use a specialised grip rod and have to increase the pull force linearly while the rod is locked. The positions of the fingers are unrestrained and freely selectable. From the finger positions and the geometry of the grip rod, a physical lever was derived which is a comprehensive measurement of the subject's grip behaviour. In this study, the involvement of the cerebellum in establishing cued force changes (CFC) was examined. The auditory stimulus was associated with a motor behaviour that has to be readjusted during an ongoing movement that already started. Moreover, cerebellar involvement on grip behaviour was examined. The results show that patients presenting with degenerating cerebellar disease (CBL) were able to elicit CFC and were additionally able to optimise grip behaviour by minimising the lever. Comparison of the results of CBL with a control group of healthy subjects showed, however, that the CFC incidence was significantly lower and the reduction of the lever was less in CBL. Hence, the cerebellum is involved not only in the classical conditioning of reflexes but also in the association of sensory stimuli with complex changes in motor behaviour. Furthermore, the cerebellum is involved in the optimisation of grip behaviour during ongoing movements. Recent studies lead to the assumption that the cerebello-reticulo-spinal pathway might be important for the reduced optimisation of grip behaviour in CBL.

Variable tunneling barriers in FEBID based PtC metal-matrix nanocomposites as a transducing element for humidity sensing.

The development of simple gas sensing concepts is still of great interest for science and technology. The demands on an ideal device would be a single-step fabrication method providing a device which is sensitive, analyte-selective, quantitative, and reversible without special operating/reformation conditions such as high temperatures or special environments. In this study we demonstrate a new gas sensing concept based on a nanosized PtC metal-matrix system fabricated in a single step via focused electron beam induced deposition (FEBID). The sensors react selectively on polar H2O molecules quantitatively and reversibly without any special reformation conditions after detection events, whereas non-polar species (O2, CO2, N2) produce no response. The key elements are isolated Pt nanograins (2-3 nm) which are embedded in a dielectric carbon matrix. The electrical transport in such materials is based on tunneling effects in the correlated variable range hopping regime, where the dielectric carbon matrix screens the electric field between the particles, which governs the final conductivity. The specific change of these dielectric properties by the physisorption of polar gas molecules (H2O) can change the tunneling probability and thus the overall conductivity, allowing their application as a simple and straightforward sensing concept.

The impact of plasmonic electrodes on the photocarrier extraction of inverted organic bulk heterojunction solar cells.

Nano-patterning the semiconducting photoactive layer/back electrode interface of organic photovoltaic devices is a widely accepted approach to enhance the power conversion efficiency through the exploitation of numerous photonic and plasmonic effects. Yet, nano-patterning the semiconductor/metal interface leads to intertwined effects that impact the optical as well as the electrical characteristic of solar cells. In this work we aim to disentangle the optical and electrical effects of a nano-structured semiconductor/metal interface on the device performance. For this, we use an inverted bulk heterojunction P3HT:PCBM solar cell structure, where the nano-patterned photoactive layer/back electrode interface is realized by patterning the active layer with sinusoidal grating profiles bearing a periodicity of 300 nm or 400 nm through imprint lithography while varying the photoactive layer thickness (L PAL ) between 90 and 400 nm. The optical and electrical device characteristics of nano-patterned solar cells are compared to the characteristics of control devices, featuring a planar photoactive layer/back electrode interface. We find that patterned solar cells show for an enhanced photocurrent generation for a L PAL above 284 nm, which is not observed when using thinner active layer thicknesses. Simulating the optical characteristic of planar and patterned devices through a finite-difference time-domain approach proves for an increased light absorption in presence of a patterned electrode interface, originating from the excitation of propagating surface plasmon and dielectric waveguide modes. Evaluation of the external quantum efficiency characteristic and the voltage dependent charge extraction characteristics of fabricated planar and patterned solar cells reveals, however, that the increased photocurrents of patterned devices do not stem from an optical enhancement but from an improved charge carrier extraction efficiency in the space charge limited extraction regime. Presented findings clearly demonstrate that the improved charge extraction efficiency of patterned solar cells is linked to the periodic surface corrugation of the (back) electrode interface. Supplementary Information: The online version contains supplementary material available at 10.1007/s00339-023-06492-6.

Contribution of the cerebellum to the coupling of grip force and pull force during an isometric precision grip task.

This study addresses the influence of the cerebellum on the performance of an isometric precision grip task. For the task, in which the process of "picking a raspberry" is simulated, grip force and pull force had to be increased linearly for a duration of 1-5 s (pull phase) to accomplish the task skillfully. The performance of 11 patients suffering from degenerative cerebellar disease was analyzed and compared with the performance of 11 age- and sex-matched healthy control subjects. Patients with cerebellar disease showed systematic deviations of the pull force slope from a linear trend, dividing the pull phase into two intervals. After an initial sharp and brief increase of pull force (first interval), patients maintained the achieved pull force level almost constant without further increase (second interval). Although controls showed changes in the pull force slope also, they increased pull force during the whole pull phase. Coupling of grip force and pull force was analyzed using stochastic frontier analysis. This technique allows covariation of grip force and the resulting pull force to be analyzed depending on the variation of the grip force. In the patients, grip force and pull force were coupled efficiently only in the first interval. During the second interval, grip force was often exaggerated compared with pull force. In conclusion, patients with cerebellar diseases have difficulties in producing smooth isometric movements and in coupling grip force and pull force efficiently.

Stimulus-dependent deliberation process in left- and right-handers obtained via current source density analysis.

The aim of the present study was to compare the activity patterns of young, healthy right- (RH, n = 25) and left-handed (LH, n = 20) subjects in high-density electroencephalograpic (EEG) recordings during a deliberation task. The deliberation task consisted of pressing one of two keys depending on a color-word Stroop task (Stroop, 1935) presented on a computer screen. Depending on the color shown and the meaning of the color word, participants responded with the index finger of the dominant or non-dominant hand. This leads to different activities in the hemispheres depending on the acting hand and on subject's handedness. Presenting the word "black" in black color, subjects were not to press any key (no-go-trial). Prior to this, subjects were tested for simple motor tasks, during which they were informed about the motor action to be performed. The temporal activity patterns obtained from RH and LH were very similar in shape and constituent components. The comparison of the three types of trials lead to the assumption that the deliberation process is based on a two-step decision: The first decision was characterized by the choice between move (match-trials, mismatch-trials) or not to move (no-go-trials). The second decision resulted in the final judgment of which index finger has to be used. The latter decision, in particular, can be tracked via the local spread of activity over the scalp. Our hypothesis is based on a comparison of activities and locations of RH and LH and yields some insights about processing a two-step decision in a deliberation task.

Somatosensory Influence on Platform-Induced Translational Vestibulo-Ocular Reflex in Vertical Direction in Humans.

The vestibulo-ocular reflex (VOR) consists of two components, the rotational VOR (rVOR) elicited by semicircular canal signals and the translational VOR (tVOR) elicited by otolith signals. Given the relevant role of the vertical tVOR in human walking, this study aimed at measuring the time delay of eye movements in relation to whole-body vertical translations in natural standing position. Twenty (13 females and 7 males) healthy, young subjects (mean 25 years) stood upright on a motor-driven platform and were exposed to sinusoidal movements while fixating a LED, positioned at a distance of 50 cm in front of the eyes. The platform motion induced a vertical translation of 2.6 cm that provoked counteracting eye movements similar to self-paced walking. The time differences between platform and eye movements indicated that the subject's timing of the extraocular motor reaction depended on stimulus frequency and number of repetitions. At low stimulus frequencies (<0.8 Hz) and small numbers of repetitions (<3), eye movements were phase advanced or in synchrony with platform movements. At higher stimulus frequencies or continuous stimulation, eye movements were phase lagged by ~40 ms. Interestingly, the timing of eye movements depended on the initial platform inclination. Starting with both feet in dorsiflexion, eye movements preceded platform movements by 137 ms, whereas starting with both feet in plantar flexion eye movement precession was only 19 ms. This suggests a remarkable influence of foot proprioceptive signals on the timing of eye movements, indicating that the dynamics of the vertical tVOR is controlled by somatosensory signals.

Dynamic torque during a precision grip task comparable to picking a raspberry.

Numerous studies have shown torque control to be an important factor in grip-force control. This study introduces a novel task which allows quantification of the dynamics of torque development while increasing grip forces during a task comparable to picking a raspberry. The performance of this task was analysed in two healthy subjects and two cerebellar patients. Individual grip forces and finger positions on a grip rod were analysed using a recently developed technique [Kutz DF, Woelfel A, Timmann D, Kolb FP. Detection of changes in grip forces on a sliding object. J Neurosci Methods 2007;166:250-8]. Levers and torques were derived from grip forces and geometric properties of the grip rod. The analysis of this task performance provides evidence that healthy subjects are able to minimise torque despite increasing grip force, whereas the cerebellar patients tested increased torque disproportionately with increasing grip forces, whereby these high torques were due primarily to the patients' inability to optimise individual finger positions on the rod. Patients tried to compensate their ataxia-based insecurity by employing higher grip forces, resulting in disproportionately higher torques and increased instability, whereupon they again increased grip force, thus establishing a vicious circle. The analysis of this task suggests that effective rehabilitation strategies must be aimed at interrupting this circle.

Spatio-Temporal Human Grip Force Analysis via Sensor Arrays.

This study describes a technique for measuring human grip forces exerted on a cylindrical object via a sensor array. Standardised resistor-based pressure sensor arrays for industrial and medical applications have been available for some time. We used a special 20 mm diameter grip rod that subjects could either move actively with their fingers in the horizontal direction or exert reactive forces against opposing forces generated in the rod by a linear motor. The sensor array film was attached to the rod by adhesive tape and covered approximately 45 cm(2) of the rod surface. The sensor density was 4/cm(2) with each sensor having a force resolution of 0.1 N. A scan across all sensors resulted in a corresponding frame containing force values at a frame repetition rate of 150/s. The force value of a given sensor was interpreted as a pixel value resulting in a false-colour image. Based on remote sensed image analysis an algorithm was developed to distinguish significant force-representing pixels from those affected by noise. This allowed tracking of the position of identified fingers in subsequent frames such that spatio-temporal grip force profiles for individual fingers could be derived. Moreover, the algorithm allowed simultaneous measurement of forces exerted without any constraints on the number of fingers or on the position of the fingers. The system is thus well suited for basic and clinical research in human physiology as well as for studies in psychophysics.

Correlation of cerebellar volume with eyeblink conditioning in healthy subjects and in patients with cerebellar cortical degeneration.

In the present study, acquisition and timing of conditioned eyeblink responses (CRs) were correlated with magnetic resonance imaging (MRI)-based cerebellar volume both in healthy human subjects and patients with cerebellar disease. Thirty-three healthy subjects and 25 patients with pure cortical cerebellar degeneration participated. Cerebellar volumes were measured for the cortex of the anterior lobe, the cortex of the posterior lobe, the white matter of the cerebellum and the cerebrum based on 3D MR images. CR parameters were assessed in a standard delay paradigm. In healthy subjects CR acquisition was significantly related to the volume of the grey matter of the posterior lobe, but neither to the volume of the grey matter of the anterior lobe, nor to the cerebellar white matter and nor to the cerebral volume. As expected, CR acquisition and volume of the cortex of the posterior lobe showed age-related decline in the controls. Furthermore, CR acquisition was significantly reduced in patients with cerebellar degeneration compared to controls. In the cerebellar group, however, no significant correlations between CR acquisition and any of the cerebellar volumes were observed. Floor effects are most likely responsible for this observation. Although CRs occurred significantly earlier in cerebellar patients compared to controls, no significant correlations between CR timing parameters and any of the cerebellar volumes were observed. Extending previous findings in healthy human subjects, age-related decline of the cerebellar cortex of the posterior lobe was related with a reduction of CR acquisition. Findings provide further evidence that the cerebellar cortex plays an important role in the acquisition of eyeblink conditioning in humans.

Detection of changes in grip forces on a sliding object.

Holding a slipping object in hand requires adjustment of grip forces. The aim of the study was to develop a method for measuring the temporal and spatial distribution of grip forces during the holding of a slipping object in the hand. A special grip rod with a measuring film containing 200 resistor-based pressure sensors equally distributed over 50 cm(2) was developed, providing a system that has a spatial resolution of 5 mm, a temporal resolution of 1/150 Hz and a force resolution 0.05 N. A force-change-detection algorithm was constructed to detect and separate pressure and position of individual fingers. The algorithm is a modification of a classical Gaussian random field theory algorithm for detecting significant data [Rogerson PA. Change detection thresholds for remotely sensed images. J Geog Syst 2002;4:85-97]. The modification takes the signal strength into account to reduce false positive detection in low grip force situations. The grip force measuring system and the force-change-detection algorithm allow measurement of the forces exerted by any number of fingers simultaneously without any constraints on finger position and are suitable for basic and clinical research in human and animal physiology as well as for psychophysics studies.

Sex differences in thermal detection and thermal pain threshold and the thermal grill illusion: a psychophysical study in young volunteers.

BACKGROUND: Sex-related differences in human thermal and pain sensitivity are the subject of controversial discussion. The goal of this study in a large number of subjects was to investigate sex differences in thermal and thermal pain perception and the thermal grill illusion (TGI) as a phenomenon reflecting crosstalk between the thermoreceptive and nociceptive systems. The thermal grill illusion is a sensation of strong, but not necessarily painful, heat often preceded by transient cold upon skin contact with spatially interlaced innocuous warm and cool stimuli. METHODS: The TGI was studied in a group of 78 female and 58 male undergraduate students and was evoked by placing the palm of the right hand on the thermal grill (20/40 °C interleaved stimulus). Sex-related thermal perception was investigated by a retrospective analysis of thermal detection and thermal pain threshold data that had been measured in student laboratory courses over 5 years (776 female and 476 male undergraduate students) using the method of quantitative sensory testing (QST). To analyse correlations between thermal pain sensitivity and the TGI, thermal pain threshold and the TGI were determined in a group of 20 female and 20 male undergraduate students. RESULTS: The TGI was more pronounced in females than males. Females were more sensitive with respect to thermal detection and thermal pain thresholds. Independent of sex, thermal detection thresholds were dependent on the baseline temperature with a specific progression of an optimum curve for cold detection threshold versus baseline temperature. The distribution of cold pain thresholds was multi-modal and sex-dependent. The more pronounced TGI in females correlated with higher cold sensitivity and cold pain sensitivity in females than in males. CONCLUSIONS: Our finding that thermal detection threshold not only differs between the sexes but is also dependent on the baseline temperature reveals a complex processing of "cold" and "warm" inputs in thermal perception. The results of the TGI experiment support the assumption that sex differences in cold-related thermoreception are responsible for sex differences in the TGI.

Timing of conditioned eyeblink responses is impaired in cerebellar patients.

In the present study, timing of conditioned eyeblink responses (CRs) was investigated in cerebellar patients and age-matched controls using a standard delay paradigm. Findings were compared with previously published data of CR incidences in the same patient population (Gerwig et al., 2003; Timmann et al., 2005). Sixteen patients with pure cortical cerebellar degeneration (spinocerebellar ataxia type 6 and idiopathic cerebellar ataxia), 14 patients with lesions within the territory of the superior cerebellar artery, and 13 patients with infarctions within the territory of the posterior inferior cerebellar artery were included. The affected cerebellar lobules and possible involvement of cerebellar nuclei were determined by three-dimensional magnetic resonance imaging (MRI) in patients with focal lesions (n = 27). Based on a voxel-by-voxel analysis, MRI lesion data were related to eyeblink conditioning data. CR incidence was significantly reduced, and CRs occurred significantly earlier in patients with cortical cerebellar degeneration and lesions of the superior cerebellum compared with controls. Incidence and timing of CRs was not impaired in patients with lesions restricted to the posterior and inferior cerebellum. Voxel-based MRI analysis revealed that cortical areas within the anterior lobe (Larsell lobule HV) were most significantly related to timing deficits, whereas reduced CR incidences were related to more caudal parts (lobule HVI) of the superior cerebellar cortex. The present data suggest that different parts of the superior cerebellar cortex may be involved in the formation of the stimulus association and appropriate timing of conditioned eyeblink responses in humans. Extracerebellar premotoneuronal disinhibition, however, is another possible explanation for changes in CR timing.

Involvement of the human cerebellum in short-term and long-term habituation of the acoustic startle response: a serial PET study.

OBJECTIVE: Numerous studies have shown an involvement of the human cerebellum in motor learning, but little is known about the role of the cerebellum in learning of unspecific aversive reactions. The present study sought to distinguish which areas of the human cerebellum and brain-stem are involved in short-term habituation (STH) and long-term habituation (LTH) of the acoustic startle response. METHODS: On 5 consecutive days 42 acoustic startle stimuli were applied each day in 8 male healthy subjects. On the first and on the fifth day of the experiment [15O]H2O PET scans were performed. RESULTS: Electromyographic recordings revealed a significant decrease of the startle response within each day (STH) and across the 5 days of the experiment (LTH). On both days a decrease of regional cerebral blood flow (rCBF) across PET scans was found in the medial cerebellum most probably reflecting reduced sensory feedback during STH. Between days an increase of rCBF in the dorsomedial pons, in the mesencephalon and in an area of the medial cerebellum was observed. These activations may reflect increased inhibition of the startle response during LTH and correspond to previous animal lesion studies. Furthermore, during LTH an increase of rCBF within the lateral cerebellum in lobule HVI/Crus I was detected. CONCLUSIONS: These results suggest that distinct parts of the medial and lateral cerebellum are involved in habituation of the acoustic startle response. Lobule HVI/Crus I most likely plays a more general role in implicit learning processes considering its involvement in several conditioning paradigms. SIGNIFICANCE: The results of the present study contribute to the understanding of cerebellar involvement in learning of unspecific aversive reactions.

Extinction of conditioned eyeblink responses in patients with cerebellar disorders.

Extinction of conditioned eyeblink responses (CRs) was analyzed in sixteen patients with pure cortical cerebellar degeneration, 14 patients with lesions within the territory of the superior cerebellar artery (SCA), 13 patients with infarctions within the territory of the posterior inferior cerebellar artery (PICA) and 45 age-matched controls. Three-dimensional (3D) magnetic resonance (MRI) data sets were acquired in patients with focal lesions to identify affected cerebellar lobules and possible involvement of nuclei. Eyeblink conditioning was performed using a standard delay protocol. At the end of the experiment 10 CS-alone trials were presented as extinction trials. Controls showed significant effects of extinction that is a significant decline comparing CR-incidences in the extinction trials and the last block of 10 trials of the paired trials. In the group of all cerebellar patients, however, no significant effects of extinction were observed. In patients with unilateral lesions effects of extinction were present on the unaffected, but not on the affected side. Deficits of extinction were observed in PICA and SCA patients both with and without involvement of cerebellar nuclei. Extending previous reports in cerebellar patients the present findings show that the ipsilateral cerebellar hemisphere contributes to extinction of conditioned eyeblink responses in humans. It cannot be ruled out, however, that impaired acquisition affected the extinction results.

Stimulus-dependent deliberation process leading to a specific motor action demonstrated via a multi-channel EEG analysis.

The aim of the study was to determine whether a deliberative process, leading to a motor action, is detectable in high density EEG recordings. Subjects were required to press one of two buttons. In a simple motor task the subject knew which button to press, whilst in a color-word Stroop task subjects had to press the right button with the right index finger when meaning and color coincided, or the left button with the left index finger when meaning and color were disparate. EEG recordings obtained during the simple motor task showed a sequence of positive (P) and negative (N) cortical potentials (P1-N1-P2) which are assumed to be related to the processing of the movement. The sequence of cortical potentials was similar in EEG recordings of subjects having to deliberate over how to respond, but the above sequence (P1-N1-P2) was preceded by slowly increasing negativity (N0), with N0 being assumed to represent the end of the deliberation process. Our data suggest the existence of neurophysiological correlates of deliberative processes.

Motor learning of cue-dependent pull-force changes during an isometric precision grip task.

The "raspberry task" represents a precision grip task that requires continuous adjustment of grip and pull forces. During this task subjects grip a specialized grip rod and have to increase the pull force linearly while the rod is locked. The aim of this study was to determine whether an associated, initially neutral cue is able to evoke pull-force changes in the raspberry task. A standard delay paradigm was used to study cued pull-force changes during an ongoing movement resulting in unloading. Pull force and EMG activity of hand and arm muscles were recorded from 13 healthy, young subjects. The cue was associated with a complex change in motor behavior. In this task, cued force changes take place more rapidly than in protective reflex systems (in median after the second presentation of the cueing stimulus). A cued force change was detectable in two-thirds of paired trials. Although the force change is produced by a decrease of the EMG activity in several grip- and pull-force-producing muscles, the most significant effect in the majority of the subjects was an increase of the activity of the flexor carpi ulnaris muscle which antagonises corresponding pull-force-producing muscles. Cued force changes require adequately and precisely controlled activation of the muscle groups involved in the movement.

Limb flexion reflex-related areas in human cerebellum.

Numerous studies have shown that the cerebellum is involved in classical conditioning of specific aversive reactions. Only few studies, however, have examined the exact localization of cerebellar areas involved in the control of unconditioned reflex responses. The present study investigated cerebellar areas, which are activated during eliciting of the limb flexion reflex in healthy controls using [15O]H2O PET. Limb flexion reflex related areas were found in vermal lobules III-VI with the local maximum in vermal lobule V. Areas of activation were more widespread compared to a voluntary foot movement and a sensory foot stimulation condition. Limb flexion reflex areas probably reflect efferent reflex modulation as well as sensory inputs from the stimulus itself and/or the reflex response.

Cerebellar representation of the eyeblink response as revealed by PET.

Blink reflex-related areas in the human cerebellum were studied using [15O]H2O PET in eight healthy subjects. Eyeblinks were evoked by airpuff stimulation and recorded via surface electrodes. PET analysis revealed a cerebellar increase of regional cerebral blood flow in vermal lobule VI and a small ipsilateral paravermal extension in the eyeblink condition compared to rest. This activation partly overlapped with areas found in recent fMRI and animal studies investigating the cerebellar involvement in control of the unconditioned and acquisition of the conditioned eyeblink response. In conclusion, vermal lobule VI extending to ipsilateral paravermal areas appears to be involved in control of the unconditioned eyeblink response.

Involvement of the human cerebellum in fear-conditioned potentiation of the acoustic startle response: a PET study.

Fear-conditioned potentiation of the startle response was used to study the role of the cerebellum in associative learning of non-specific aversive reactions in healthy human subjects using PET. Prior PET scanning initially neutral light stimuli were paired with painful electric shocks (fear-conditioning phase). Four PET-scans each were performed with presentation of acoustic startle stimuli (T), fear-conditioned light stimuli (L) or acoustic stimuli paired with light (LT, potentation phase). As a measure of fear-conditioning subtraction of condition T from LT revealed an increase of regional cerebellar blood flow (rCBF) in the left cerebellar hemisphere. Subtraction of condition L from LT, as a measure of fear-conditioned potentiation, revealed an increase of rCBF in the medial cerebellum. Different parts of the cerebellum appear to be involved in this form of motor associative learning.