Assessment of rapeseed oil body (oleosome) lipolytic activity as an effective predictor of emulsion purity and stability
Chirico, Simone De; Bari, Vincenzo di; Romero Guzmán, María Juliana ; Nikiforidis, Constantinos V. ; Foster, Tim ; Gray, David - \ 2020
Food Chemistry 316 (2020). - ISSN 0308-8146
Lipolytic activity - Oil bodies - Purity - Rapeseed - Stability
The lipolytic activity in oil body creams as affected by recovery and washing protocols was investigated. The effect of thermal treatment on the hydrolytic activity and physical stability of fresh and aged (up to 30 days) oil body emulsions was studied. The use of alkaline pH solutions (9.5) to soak and grind rapeseeds were more effective reducing the contamination of oil body material from seed proteins/enzymes, compared with neutral pHs. Soaking and grinding seeds with a NaHCO3 solution (0.1 M, pH 9.5) yielded oil bodies with a similar composition to those prepared in urea (9 M); however, the physical stability over storage was compromised due to the presence of hydrolytic enzymes. Heating a dispersion of oil bodies for 6 mins at 95 °C did not alter the physical properties of oil bodies and significantly reduced lipolytic activity (>90% enzyme inactivation), resulting in a stable emulsion.
Temporal Limits of Visual Motion Processing: Psychophysics and Neurophysiology
Borghuis, Bart G. ; Tadin, Duje ; Lankheet, Martin J.M. ; Lappin, Joseph S. ; Grind, Wim A. van de - \ 2019
Vision 3 (2019)1. - ISSN 2411-5150 - 17 p.
Under optimal conditions, just 3–6 ms of visual stimulation suffices for humans to see motion. Motion perception on this timescale implies that the visual system under these conditions reliably encodes, transmits, and processes neural signals with near-millisecond precision. Motivated by in vitro evidence for high temporal precision of motion signals in the primate retina, we investigated how neuronal and perceptual limits of motion encoding relate. Specifically, we examined the correspondence between the time scale at which cat retinal ganglion cells in vivo represent motion information and temporal thresholds for human motion discrimination. The timescale for motion encoding by ganglion cells ranged from 4.6 to 91 ms, and depended non-linearly on temporal frequency, but not on contrast. Human psychophysics revealed that minimal stimulus durations required for perceiving motion direction were similarly brief, 5.6–65 ms, and similarly depended on temporal frequency but, above ~10%, not on contrast. Notably, physiological and psychophysical measurements corresponded closely throughout (r = 0.99), despite more than a 20-fold variation in both human thresholds and optimal timescales for motion encoding in the retina. The match in absolute values of the neurophysiological and psychophysical data may be taken to indicate that from the lateral geniculate nucleus (LGN) through to the level of perception little temporal precision is lost. However, we also show that integrating responses from multiple neurons can improve temporal resolution, and this potential trade-off between spatial and temporal resolution would allow for loss of temporal resolution after the LGN. While the extent of neuronal integration cannot be determined from either our human sychophysical or neurophysiological experiments and its contribution to the measured temporal resolution is unknown, our results demonstrate a striking similarity in stimulus dependence between the temporal fidelity established in the retina and the temporal limits of human motion discrimination.
Advantages of concurrent use of multiple software frameworks in water quality modelling using a database approach
Gerven, L.P.A. van; Brederveld, R.J. ; Klein, J.J.M. de; DeAngelis, D.L. ; Downing, A.S. ; Faber, M. ; Gerla, D.J. ; Hoen, J. 't; Janse, J.H. ; Janssen, A.B.G. ; Jeuken, Michel ; Kooi, B.W. ; Kuiper, J.J. ; Lischke, B. ; Liu, Sien ; Petzoldt, Thomas ; Schep, S.A. ; Teurlincx, Sven ; Thiange, C. ; Trolle, D. ; Nes, E.H. van; Mooij, W.M. - \ 2015
Fundamental and Applied Limnology 186 (2015)1-2. - ISSN 1863-9135 - p. 5 - 20.
Water quality modelling deals with multidisciplinary questions ranging from fundamental to applied. Addressing this broad range of questions requires multiple analysis techniques and therefore multiple frameworks. Through the recently developed database approach to modelling (DATM), it has become possible to run a model in multiple software frameworks without much overhead. Here we apply DATM to the ecosystem model for ditches. PCDitch and its twin model for shallow lakes PCLake. Using DATM, we run these models in six frameworks (ACSL, DELWAQ, DUFLOW, GRIND for MATLAB, OSIRIS and R), and report on the possible model analyses with tools provided by each framework. We conclude that the dynamic link between frameworks and models resulting from DATM has the following main advantages: it allows one to use the framework one is familiar with for most model analyses and eases switching between frameworks for complementary model analyses, including the switch between a 0-D and 1-D to 3-D setting. Moreover, the strength of each framework – including runtime performance – can now be easily exploited. We envision that a community-based further development of the concept can contribute to the future development of water quality modelling, not only by addressing multidisciplinary questions but also by facilitating the exchange of models and process formulations within the community of water quality modellers.
Een evaluatiekader voor ontgrondingen : Een studie naar de maatschappelijke gevolgen van ontgrondingen
Haaften, M. ; Heijman, W.J.M. ; Rietveld, M. - \ 2015
Water Governance 5 (2015)3. - ISSN 2211-0224 - p. 24 - 30.
markteconomie - regionaal beleid - maatschappelijk draagvlak - grondverzet - effecten - nadelige gevolgen - vergunningen - gelderland - market economics - regional policy - public support - earth moving - effects - adverse effects - permits - gelderland
Op 1 februari 2008 verdween de plicht van provincies om van tevoren vastgestelde hoeveelheden zand en grind te leveren Deze beleidswijziging van taakstelling naar marktwerking werd doorgevoerd vanwege een slechte voorspelbaarheid van de behoefte aan zand en grind, een tanend maatschappelijk draagvlak en de wens om beleidskosten te verminderen. In het nieuwe beleid is economisch belang gekoppeld aan het creëren van maatschappelijk draagvlak. Overheden, omwonenden en bedrijven leveren vanuit hun betrokkenheid een bijdrage aan de afweging van gevolgen van ontgrondingen op maatschappelijk en economisch terrein. Deze gevolgen doen zich op kortere of langere termijn voor, op lokaal, regionaal en nationaal niveau. Een afwegingskader dat de gevolgen van het ontgronden beschrijft, inzichtelijk maakt en beoordeelt, ontbreekt tot op heden. Hetgeen het besluitvormingsproces inzake het verlenen van ontgrondingvergunningen niet transparant maakt. Het doel van dit artikel is tweeledig. Eerst worden de mogelijke gevolgen van ontgrondingen geïnventariseerd, daarna wordt ex post geëvalueerd hoe de afweging van gevolgen een plaats heeft gekregen in het beleid van de Provincie Gelderland. Het artikel besluit met een aantal aanbevelingen ter vergroting van het maatschappelijk draagvlak voor ontgrondingen.
Mogelijk verband tussen het storten van zeegrind en sterfte van mosselen op nabij gelegen percelen Hammen 62, 63 en 64
Smaal, A.C. - \ 2015
Yerseke : IMARES (Rapport / IMARES C105/15) - 24
mossels - oeverecosystemen - oeverbescherming van rivieren - aquatische ecosystemen - oosterschelde - grind - mussels - riparian ecosystems - riverbank protection - aquatic ecosystems - eastern scheldt - gravel
In november 2014 is sterfte vastgesteld van mosselen op de kweekpercelen Hammen 62, 63 en 64 die zijn gelegen naast de locatie waar in september 2014 bestortingen zijn uitgevoerd met zeegrind ten behoeve van de vooroeververdediging. De vraag is in hoeverre er een causaal verband aannemelijk is tussen de gevolgen van het uitvoeren van de bestortingen en de door kwekers en visserijkundig ambtenaar geconstateerde mosselsterfte.
Effect van vooroeversuppletie met zeegrind op groei en ontwikkeling van mosselen in Oosterschelde
Wijsman, J.W.M. ; Brummelhuis, E.B.M. - \ 2015
Yerseke : IMARES (Rapport / IMARES Wageningen UR C063/15) - 32
mossels - grind - zeeland - oosterschelde - oevers - oeverbescherming van rivieren - dijken - mussels - gravel - zeeland - eastern scheldt - shores - riverbank protection - dykes
In het najaar van 2014 zijn er bij de locatie Zierikzee en Burghsluis vooroeververdedigings-werkzaamheden uitgevoerd met zeegrind. Bij het storten van het zeegrind kan slib vrijkomen dat effect kan hebben op de efficiëntie van de voedselopname van de mosselen en daarmee kan leiden tot groeivertraging. De verzamelde gegevens zijn daarom gebruikt om te onderzoeken of er groeivertraging is opgetreden bij de mosselen in de mandjes zijn uitgezet op 5 locaties (2 locaties bij Zierikzee, 2 bij Burghsluis en 1 als referentie bij Neeltje Jans), tijdens het storten van zeegrind in het kader van de werkzaamheden aan de vooroever bij Zierikzee en Burghsluis.
Serving many at once: How a database approach can create unity in dynamical ecosystem modelling
Mooij, W.M. ; Brederveld, R.J. ; Klein, J.J.M. de; DeAngelis, D.L. ; Downing, A.S. ; Faber, M. ; Gerla, D.J. ; Hipsey, M.R. ; Hoen, J. 't; Janse, J.H. ; Janssen, A.B.G. ; Jeuken, M. ; Kooi, B.W. ; Lischke, B. ; Petzoldt, T. ; Postma, L. ; Schep, S.A. ; Scholten, H. ; Teurlincx, S. ; Thiange, C. ; Trolle, D. ; Dam, A.A. van; Gerven, L.P.A. van; Nes, E.H. van; Kuiper, J.J. - \ 2014
Environmental Modelling & Software 61 (2014). - ISSN 1364-8152 - p. 266 - 273.
shallow lakes - simulation - eutrophication - management - package - pclake
Simulation modelling in ecology is a field that is becoming increasingly compartmentalized. Here we propose a Database Approach To Modelling (DATM) to create unity in dynamical ecosystem modelling with differential equations. In this approach the storage of ecological knowledge is independent of the language and platform in which the model will be run. To create an instance of the model, the information in the database is translated and augmented with the language and platform specifics. This process is automated so that a new instance can be created each time the database is updated. We describe the approach using the simple Lotka-Volterra model and the complex ecosystem model for shallow lakes PCLake, which we automatically implement in the frameworks OSIRIS, GRIND for MATLAB, ACSL, R, DUFLOW and DELWAQ. A clear advantage of working in a database is the overview it provides. The simplicity of the approach only adds to its elegance. © 2014 The Authors.
Winnen of verzanden : een studie naar de gevolgen van ontgrondingen
Haaften, M.A. van; Rietveld, M.P. ; Heijman, W.J.M. - \ 2014
Wageningen : Wageningen UR, Wetenschapswinkel (Rapport / Wageningen UR, Wetenschapswinkel 307) - ISBN 9789461738783 - 49
landschapsplanning - landschap - belevingswaarde - zandafgravingen - regionale planning - publieke participatie - regelingen - land van maas en waal - Nederland - landscape planning - landscape - experiential value - sand pits - regional planning - public participation - regulations - land van maas en waal - Netherlands
De winning van delfstoffen uit de oppervlakte, het ontgronden, veroorzaakt een onomkeerbare verandering van het landschap. Naast het winnen van zand (ontzanden) kan het daarbij gaan om klei, grind, mergel en schelpen. Het proces om tot een ontgronding te komen is een langdurig traject waarbij verschillende belangen van ontgronder, gemeente en bewoners tegen elkaar dienen te worden afgewogen. Een groep inwoners in Deest maakt zich zorgen om de ontgrondingen bij Deest: de Ganzenkuil (gerealiseerd), de Uivermeertjes (deels gerealiseerd deels in bedrijf) en de voorgenomen planvorming omtrent de Deesterkaap, Geertjesgolf en voorhaven. Deze bewoners verenigd in de ‘Stichting Goeie Gronde’ en de ontgronder Sagrex zijn betrokken geweest bij verschillende procedures bij de Raad van State met betrekking tot ontgrondingen, met wisselende uitkomsten. De Stichting Goeie Gronde heeft de Wetenschapswinkel van Wageningen UR gevraagd onderzoek te doen naar de gevolgen van ontgrondingen in Deest voor de omgeving en haar bewoners.
Protease digestion from wheat stillage within a dry grind ethanol facility
Bals, B. ; Brehmer, B. ; Dale, B. ; Sanders, J.P.M. - \ 2011
Biotechnology Progress 27 (2011)2. - ISSN 8756-7938 - p. 428 - 434.
distillers grains - extraction - proteins - optimization - hydrolysis - solubles - alcohol - options - water
As the current starch based ethanol market increases at its rapid pace, finding new markets for the primary coproduct, distiller's grains, has gained considerable interest. One possibility is to isolate the protein-rich fraction for use as precursors to biochemicals and bioplastics, further decreasing fossil fuel consumption. This research focuses on enzymatic extraction of protein peptides from wheat heavy stillage using commercially available proteases. The energy saved due to this process ranged from ~1.5 to 3.0 GJ/ton wheat stillage compared to fossil fuel-based chemicals. Using Protex 6L (Genencor), ~57% of the protein in the stillage was soluble 24 h after protease addition at 0.1% w/w loading. Of these proteins, ~32% were already soluble, indicating the importance of using wet heavy stillage as the feedstock rather than dried distiller's grains. Peptide size was less than 6 kDa. Further improvements in protein removal may be obtained through a fed batch addition of protease and improved protease cocktails
|Simultaneity versus asynchrony of visual motion and luminance changes
Lankheet, M.J.M. ; Grind, W.A. van de - \ 2010
In: Space and Time in Perception and Action / Nijhawan, R., Khurana, B., Cambridge, UK : Cambridge University Press - ISBN 9780521863186 - p. 301 - 321.
Improving the corn-ethanol industry: studying protein separation techniques to obtain higher value added product options for distillers grains
Brehmer, B. ; Bals, B. ; Sanders, J.P.M. ; Dale, B. - \ 2008
Biotechnology and Bioengineering 101 (2008)1. - ISSN 0006-3592 - p. 49 - 61.
enzymatic-hydrolysis - pretreatment - biomass - energy - stover
Currently in America the biofuel ethanol is primarily being produced by the dry grind technique to obtain the starch contained in the corn grains and subsequently subjected to fermentation. This so-called 1st generation technology has two setbacks; first the lingering debate whether its life cycle contributes to a reduction of fossil fuels and the animal feed sectors future supply/demand imbalance caused by the co-product dry distillers grains (DDGS). Additional utilization of the cellulosic components and separation of the proteins for use as chemical precursors have the potential to alleviate both setbacks. Several different corn feedstock layouts were treated with 2nd generation ammonia fiber expansion (AFEX) pre-treatment technology and tested for protein separation options (protease solubilization). The resulting system has the potential to greatly improve ethanol yields with lower bioprocessing energy costs and satisfy a significant portion of the organic chemical industry.
Temporal interactions in direction-selective complex cells of area 18 and the posteromedial lateral suprasylvian cortex (PMLS) of the cat
Vajda, Ildikó ; Borghuis, Bart G. ; De Grind, Wim A. Van; Lankheet, Martin J.M. - \ 2006
Visual Neuroscience 23 (2006)2. - ISSN 0952-5238 - p. 233 - 246.
Cat extrastriate area - Motion opponency - Motion vision - Random pixel array - Second-order reverse correlation
Temporal interactions in direction-sensitive complex cells in area 18 and the posteromedial lateral suprasylvian cortex (PMLS) were studied using a reverse correlation method. Reverse correlograms to combinations of two temporally separated motion directions were examined and compared in the two areas. A comparison to the first-order reverse correlograms allowed us to identify nonlinear suppression or facilitation due to pairwise combinations of motion directions. Results for area 18 and PMLS were veiy different. Area 18 showed a single type of nonlinear behavior: similar directions facilitated and opposite directions suppressed spike probability. This effect was most pronounced for motion steps that followed each other immediately and decreased with increasing delay between steps. In PMLS, the picture was much more diverse. Some cells exhibited nonlinear interactions, that were opposite to those in area 18 (facilitation for opposite directions and suppression for similar ones), while the majority did not show a systematic interaction profile. We conclude that nonlinear second-order reverse correlation characteristics reveal different functional properties, despite similarities in the first-order reverse correlation profiles. Directional interactions in time revealed optimal integration of similar directions in area 18, but motion opponency - at least in some cells - in PMLS.
Spatio-temporal requirements for direction selectivity in area 18 and PMLS complex cells
Vajda, Ildikó ; Lankheet, Martin J.M. ; De Grind, Wim A. Van - \ 2005
Vision Research 45 (2005)13. - ISSN 0042-6989 - p. 1769 - 1779.
Cat extrastriate area - Motion vision - Random pixel array - Single step pattern lifetime - Spatio-temporal characteristics
The spatio-temporal requirements for direction selectivity were studied in two extrastriate motion processing areas in the cat, area 18 and the posteromedial lateral suprasylvian cortex (PMLS). Direction, velocity and pixel size of random pixel arrays (RPA) were adjusted for each neuron and direction selectivity was measured as a function of step size and delay for a given optimal velocity. A subset of direction selective complex cells in area 18 was tuned to intermediate step size and delay combinations rather than the smoothest motion (band-pass cells). Other area 18 complex cells responded best to the smallest value of step size and delay (low-pass cells). Tuning varied with the pixel size of the RPA. Cells with tuning for smaller pixels favoured a preference for non-smooth motion. Area 18 cells with lower spatial resolution showed larger optimal and maximal step sizes. For a subset of the cells in area 18, we measured direction selectivity for extensive step-delay combinations, covering multiple velocities. Results showed that most cells were tuned to narrow range of step-delay combinations, and that the optimal step size was independent of temporal delay. Direction selective complex cells in PMLS were tuned to larger pixel sizes than those in area 18, although the distributions did overlap. In contrast to area 18, PMLS cells preferred the smoothest motion, irrespective of RPA pixel size.
Binocular correlation does not improve coherence detection for fronto-parallel motion
Muller, Chris ; Lankheet, Martin J.M. ; De Grind, Wim A. Van - \ 2004
Vision Research 44 (2004)16. - ISSN 0042-6989 - p. 1961 - 1969.
We studied the low-level interactions between motion coherence detection and binocular correlation detection. It is well-established that e.g. depth information from motion parallax and from binocular disparities is effectively integrated. The question we aimed to answer is whether such interactions also exist at the very first correlation level that both mechanisms might have in common. First we quantitatively compared motion coherence detection and binocular correlation detection using similar stimuli (random pixels arrays, RPAs) and the same noise masking paradigm (luminance signal to noise ratio, LSNR). This showed that human observers are much more sensitive to motion than to binocular correlation. Adding noise therefore has a much stronger effect on binocular correlation than on motion detection. Next we manipulated the shape of the stimulus aperture to equalize LSNR thresholds for motion and binocular correlation. Motion sensitivity could be progressively reduced by shortening the length of the motion path, while keeping the aperture area constant. Changing the shape of the aperture did not affect binocular correlation sensitivity. A 'balanced' stimulus, one with equal strengths of motion and binocular correlation signals was then used to study the mutual interactions. In accordance with previous results, motion was found to greatly facilitate binocular correlation. Binocular correlation, however did not facilitate motion detection. We conclude that interactions are asymmetrical; fronto-parallel motion is primarily detected monocularly and this information can then be used to facilitate binocular correlation, but binocular correlation cannot improve motion sensitivity.
Dynamics of directional selectivity in area 18 and PMLS of the cat
Vajdal, Ildikó ; Lankheet, Martin J.M. ; Borghuis, Bart G. ; De Grind, Wim A. Van - \ 2004
Cerebral Cortex 14 (2004)7. - ISSN 1047-3211 - p. 759 - 767.
Cat extrastriate area - Motion vision - Random pixel array - Reverse correlation - Single unit recording
Visual latencies and temporal dynamics of area 18 and PMLS direction-selective complex cells were defined with a reverse correlation method. The method allowed us to analyze the time course of responses to motion steps, without confounding temporal integration effects. Several measures of response latency and direction tuning dynamics were quantified: optimal latency (OL), latency of first and last significant responses (FSR, LSR), the increase and decrease of direction sensitivity in time, and the change of direction tuning in time. FSR, OL and LSR values for PMLS and area 18 largely overlapped. The small differences in mean latencies (3-4 ms for FSR and OL and 11.9 ms for the LSR) were not statistically significant. All cells in area 18 and the vast majority of cells in PMLS showed no systematic changes in preferred direction (monophasic neurons). In PMLS 5 out of 41 cells showed a reversal of preferred direction after ∼56 ms relative to their OL (biphasic neurons). Monophasic cells showed no systematic changes in direction tuning width during the interval from FSR to LSR. In both areas, development of direction sensitivity was significantly faster than return to the non direction sensitive state, but no significant difference was found between the two areas. We conclude that, for the monophasic type of direction-selective complex cells, the dynamics of primary motion processing are highly comparable for area 18 and PMLS. This suggests that motion information is predominantly processed in parallel, presumably based on input from the fast conducting thalamocortical Y-pathway.
A gain-control model relating nulling results to the duration of dynamic motion aftereffects
Grind, W.A. Van de; Lankheet, M.J.M. ; Tao, R. - \ 2003
Vision Research 43 (2003)2. - ISSN 0042-6989 - p. 117 - 133.
Aftereffect-nulling - Dynamic MAE - Gain-control model - MAE-duration
Strength of the motion aftereffect (MAE) is most often quantified by its duration, a high-variance and rather 'subjective' measure. With the help of an automatic gain-control model we quantitatively relate nulling-thresholds, adaptation strength, direction discrimination threshold, and duration of the dynamic MAE (dMAE). This shows how the nulling threshold, a more objective two-alternative forced-choice measure, relates to the same system property as MAE-durations. Two psychophysical experiments to test the model use moving random-pixel-arrays with an adjustable luminance signal-to-noise ratio. We measure MAE-duration as a function of adaptation strength and compare the results to the model prediction. We then do the same for nulling-thresholds. Model predictions are strongly supported by the psychophysical findings. In a third experiment we test formulae coupling nulling threshold, MAE-duration, and direction-discrimination thresholds, by measuring these quantities as a function of speed. For the medium-to-high speed range of these experiments we found that nulling thresholds increase and dMAE-durations decrease about linearly, whereas direction discrimination thresholds increase exponentially with speed. The model description then suggests that the motion-gain decreases, while the noise-gain and model's threshold increase with speed.
The motion reverse correlation (MRC) method:: A linear systems approach in the motion domain
Borghuis, Bart G. ; Perge, János A. ; Vajda, Ildikó ; Wezel, Richard J.A. Van; De Grind, Wim A. Van; Lankheet, Martin J.M. - \ 2003
Journal of Neuroscience Methods 123 (2003)2. - ISSN 0165-0270 - p. 153 - 166.
Area MT - Cat - Direction selectivity - Monkey - Motion vision - Reverse correlation - Visual cortex
We introduce the motion reverse correlation method (MRC), a novel stimulus paradigm based on a random sequence of motion impulses. The method is tailored to investigate the spatio-temporal dynamics of motion selectivity in cells responding to moving random dot patterns. Effectiveness of the MRC method is illustrated with results obtained from recordings in both anesthetized cats and an awake, fixating macaque monkey. Motion tuning functions are computed by reverse correlating the response of single cells with a rapid sequence of displacements of a random pixel array (RPA). Significant correlations between the cell's responses and various aspects of stimulus motion are obtained at high temporal resolution. These correlations provide a detailed description of the temporal dynamics of, for example, direction tuning and velocity tuning. In addition, with a spatial array of independently moving RPAs, the MRC method can be used to measure spatial as well as temporal receptive field properties. We demonstrate that MRC serves as a powerful and time-efficient tool for quantifying receptive field properties of motion selective cells that yields temporal information that cannot be derived from existing methods.
Velocity dependence of the interocular transfer of dynamic motion aftereffects
Tao, Ran ; Lankheet, Martin J.M. ; Grind, Wim A. Van de; Wezel, Richard J.A. Van - \ 2003
Perception 32 (2003)7. - ISSN 0301-0066 - p. 855 - 866.
It is well established that motion aftereffects (MAEs) can show interocular transfer (IOT); that is, motion adaptation in one eye can give a MAE in the other eye. Different quantification methods and different test stimuli have been shown to give different IOT magnitudes, varying from no to almost full IOT. In this study, we examine to what extent IOT of the dynamic MAE (dMAE), that is the MAE seen with a dynamic noise test pattern, varies with velocity of the adaptation stimulus. We measured strength of dMAE by a nulling method. The aftereffect induced by adaptation to a moving random-pixel array was compensated (nulled), during a brief dynamic test period, by the same kind of motion stimulus of variable luminance signal-to-noise ratio (LSNR). The LSNR nulling value was determined in a Quest-staircase procedure. We found that velocity has a strong effect on the magnitude of IOT for the dMAE. For increasing speeds from 1.5 deg s-1 to 24 deg s-1 average IOT values increased about linearly from 18% to 63% or from 32% to 83%, depending on IOT definition. The finding that dMAEs transfer to an increasing extent as speed increases, suggests that binocular cells play a more dominant role at higher speeds.
Spatio-temporal tuning of motion coherence detection at different luminance levels
Lankheet, M.J.M. ; Doorn, A.J. Van; De Grind, W.A. Van - \ 2002
Vision Research 42 (2002)1. - ISSN 0042-6989 - p. 65 - 73.
Coherence thresholds - Dark adaptation - Human - Luminance - Motion detection - Spatio-temporal tuning
We studied effects of dark adaptation on spatial and temporal tuning for motion coherence detection. We compared tuning for step size and delay for moving random pixel arrays (RPAs) at two adaptation levels, one light adapted (50 cd/m2) and the other relatively dark adapted (0.05 cd/m2). To study coherence detection rather than contrast detection, RPAs were scaled for equal contrast detection at each luminance level, and a signal-to-noise ratio paradigm was used in which the RPA is always at a fixed, supra-threshold contrast level. The noise consists of a spatio-temporally incoherent RPA added to the moving RPA on a pixel-by-pixel basis. Spatial and temporal limits for coherence detection were measured using a single step pattern lifetime stimulus, in which patterns on alternate frames make a coherent step and are being refreshed. Therefore, the stimulus contains coherent motion at a single combination of step size and delay only. The main effect of dark adaptation is a large shift in step size, slightly less than the adjustment of spatial scale required for maintaining equal contrast sensitivity. A similar change of preferred step size occurs also for scaled stimuli at a light-adapted level, indicating that the spatial effect is not directly linked to dark adaptation, but more generally related to changes in the available low-level spatial information. Dark-adaptation shifts temporal tuning by about a factor of 2. Long delays are more effective at low luminance levels, whereas short delays no longer support motion coherence detection. Luminance-invariant velocity tuning curves, as reported previously [Lankheet, M.J.M., van Doorn, A.J., Bouman, M.A., & van de Grind, W.A. (2000) Motion coherence detection as a function of luminance in human central vision. Vision Research, 40, 3599-3611], result from recruitment of different sets of motion detectors, and an adjustment of their temporal properties.
On the velocity tuning of area 18 complex cell responses to moving textures
Vajda, Ildikó ; Lankheet, Martin J.M. ; Leeuwen, Tessa M. Van; De Grind, Wim A. Van - \ 2002
Visual Neuroscience 19 (2002)5. - ISSN 0952-5238 - p. 651 - 659.
Area 18 - Cat visual cortex - Complex cell - Space-time separability - Texture motion
Unlike simple cells, complex cells of area 18 give a directionally selective response to motion of random textures, indicating that they may play a special role in motion detection. We therefore investigated how texture motion, and especially its velocity, is represented by area 18 complex cells. Do these cells have separable spatial and temporal tunings or are these nonseparable? To answer this question, we measured responses to moving random pixel arrays as a function of both pixel size and velocity, for a set of 63 directionally selective complex cells. Complex cells generally responded to a fairly wide range of pixel sizes and velocities. Variations in pixel size of the random pixel array only caused minor changes in the cells' preferred velocity. For nearly all cells the data much better fitted a model in which pixel size and velocity act separately, than a model in which pixel size and velocity interact so as to keep temporal-frequency sensitivity constant. Our conclusion is that the studied population of special complex cells in area 18 are true motion detectors, rather than temporal-frequency tuned neurons.