5,079 research outputs found
The lowest spatial frequency channel determines brightness perception
No full textThis study investigates the role played by individual spatial scales in determining the apparent brightness of greyscale patterns. We measured the perceived difference in brightness across an edge in the presence of notch filtering and high-pass filtering for two stimulus configurations, one that elicits the perception of transparency and one that appears opaque. For both stimulus configurations, the apparent brightness of the surfaces delimited by the border decreased monotonically with progressive (ideal) high-pass filtering, with a critical cut-off at I c/deg. Using two octave ideal notch filtering, the maximum detrimental effect on apparent brightness was observed at about I c/deg. Critical frequencies for apparent brightness did not vary with contrast, viewing distance, or surface size, suggesting that apparent brightness is determined by the channel tuned at I c/deg. Modelling the data with the local energy model [Morrone, M. C., & Burr, D. C. (1988). Feature detection in human vision: a phase dependent energy model. Proceedings of the Royal Society (London), B235, 221-245] at I c/deg confirmed the suggestion that this channel mediates apparent brightness for both opaque and transparent borders, with no need for pooling or integration across spatial channels. (C) 2007 Elsevier Ltd. All rights reserved
Compression of time during smooth pursuit eye movements
No full textHumans have a clear sense for the passage of time but while implicit motor timing is quite accurate explicit timing is prone to distortions particularly during action (Wenke & Haggard 2009) and saccadic eye movements (Morrone Ross & Burr 2005) Here we investigated whether perceived duration is also affected by the execution of smooth pursuit eye movements showing a compression of apparent duration similar to that observed during saccades To this end we presented two brief bars that marked intervals between 100 and 300 ms and asked subjects to judge their duration during fixation and pursuit We found a compression of perceived duration for bars modulated in luminance contrast of about 32% and for bars modulated in chromatic contrast of 14% during pursuit compared to fixation Interestingly Weber ratios were similar for fixation and pursuit if they are expressed as ratio between JND and perceived duration This compression was constant for pursuit speeds from 7 to 14 deg/s and did not occur for Intervals marked by auditory events These results argue for a modality-specific component in the processing of temporal information (C) 2010 Elsevier Ltd All rights reserve
The role of perceptual learning on modality-specific visual attentional effects
No full textMorrone et al. [Morrone, M. C., Denti, V., & Spinelli, D. (2002). Color and luminance contrasts attract independent attention. Current Biology, 12, 1134-1137] reported that the detrimental effect on contrast discrimination thresholds of performing a concomitant task is modality specific: performing a secondary luminance task has no effect on colour contrast thresholds, and vice versa. Here we confirm this result with a novel task involving learning of spatial position, and go on to show that it is not specific to the cardinal colour axes: secondary tasks with red-green stimuli impede performance on a blue-yellow task and vice versa. We further show that the attentional effect can be abolished with continued training over 2-4 training days (2-20 training sessions), and that the effect of learning is transferable to new target positions. Given the finding of transference, we discuss the possibility that V4 is a site of plasticity for both stimulus types, and that the separation is due to a luminance-colour separation within this cortical area
Auditory and tactile signals combine to influence vision during binocular rivalry
No full textResolution of perceptual ambiguity is a major function of cross-modal interactions, making the study of bistable perception in multisensory contexts a powerful and revealing tool. We previously used binocular rivalry, a visual bistable phenomenon, to show that touch can specifically interact with vision to resolve spatial conflict between the eyes (Lunghi, Binda and Morrone, 2010). Here we investigate whether auditory and tactile stimuli can influence binocular rivalry generated by interocular temporal conflict. Using visual stimuli of different temporal frequencies (spatio-temporal noise filtered at 3.75 or at 15 Hz) to produce visual perceptual alternations, we added an amplitude modulated sound or a vibration that was congruent with one or the other visual temporal frequencies. We found that auditory and tactile stimulation interacted with binocular rivalry by promoting dominance of the congruent visual stimulus. This effect depended on the strength of the auditory/tactile stimulus, and was absent when a modulation depth declined to 33%. However, when auditory and tactile stimuli that were too weak on their own to bias binocular rivalry were combined, their influence over vision was very strong, suggesting the auditory and tactile temporal signals were summated. When auditory and tactile stimuli were presented at maximum strength, but temporally in anti-phase, they had no influence over vision, a null effect that again suggests audio-tactile summation in the temporal domain. These results indicate a functional link between auditory and tactile low temporal frequency channels, suggesting the existence of common neural substrates for the two sensory modalities
Large receptive fields for optic flow detection in humans
No full textWe used a psychophysical summation technique to study the propel-ties of detectors tuned to radial, circular and translational motion, and to determine the spatial extent of their receptive fields. Signal-to-noise motion thresholds were measured for patterns curtailed spatially in various ways. Sensitivity for radial, circular and translational motion increased with stimulus area at a rate predicted by an ideal integrator. When sectors of noise were added to the stimulus; sensitivity decreased at a rate consistent with an ideal integrator. Summation was tested for large annular stimuli, and shown to hold up to 70 degrees in some cases, suggesting very large receptive fields for this type of motion (consistent with the physiology of neurones in the dorsal region of the medial superior temporal area (MSTd)). This is a far greater area than observed for summation of contrast sensitivity to gratings (Anderson SJ and Burr DC, Vis Res 1987;29:621-635, and to this type of stimuli (Morrone MC, Burr DC and Vaina LM, Nature 1995;376:507-509, consistent with the suggestion that the two techniques examine different levels of motion analysis. (C) 1998 Elsevier Science Ltd. All rights reserved
Motion analysis by feature tracking
No full textWe have developed a two-stage model of motion perception that identifies moving spatial features and computes their velocity, achieving both high spatial localisation and reliable estimates of velocity. Features are detected in each frame by locating the peaks of the spatial local energy functions, as for stationary images (Morrone MC and Burr DC. Proc R Soc Lend 1988;B235:221-245.). The energy functions are calculated for different scales and orientations, and integrated within a temporal Gaussian window. The velocity of features is determined by the direction of maximal elongation of the energy in space-time, evaluated by calculating the three characteristic curvatures of the energy at each feature point. To circumvent the aperture problem, the energy maps are blurred in space by various amounts. and velocity is computed separately for each spatial blur. The Weber fraction of the local curvatures (curvature contrast) describes the spatio-temporal energy elongation at each feature point, giving a reliability index for each velocity estimate. For each point, the velocity of the spatial blur that yielded the highest curvature contrast was selected, with no further constraints, such as rigidity of motion. Dynamic recruitment of operators of different size allows maximum flexibility of the analysis, allowing it to simulate human visual performance in the detection of noise images, transparent motion, some motion illusions, and second-order motion. (C) 1998 Elsevier Science Ltd. All rights reserved
THERMAL PLASMA SYSTEM APPLIED TO DESTROY C-BASED POLLUTANTS
No full textAir pollution resulting from engines fueled by low quality oils (e.g. HFO) is considered responsible for around 400,000 premature deaths per year worldwide, at an annual cost to society of more than €58 billion. Moreover, the utilization of fossil fuels increases the GHG gases emission in the atmosphere. In relation to maritime sector, the main sources of C-based pollutants and GHGs gases, other than particulate matter (PM), are incinerators and engines. Engines fueled by HFO emit carbon dioxide, hydrocarbons and C-based particulate this latter with an emission factor of 0.56-2.21 g/kWh; engines fueled by LNG or LNG/HFO emit carbon dioxide, a reduced amount of C-based particulate but a larger amount of other methane, due to the methane slip phenomenon. The release of methane into atmosphere results in an increase of GHG impact, larger than the case of LFO use. This paper reports a quantitative assessment of the GHG impact due to methane slip for a commercial 18.3 MW engine and proposes a system to promote the oxidation of unconverted hydrocarbons downstream the turbocharger exit. The proposed system is based on the thermal plasma conversion: the size of an industrial equipment and that of the corresponding down-scaled experimental set-up is described. The plasma converting reactor (PCR) is applicable to flue gas with a good effectiveness in hydrocarbons conversion abatement but the electricity cost necessary to run it with large gas flow rates should be economically unfeasible. Thus, an estimation of electricity cost and capex is given
Spatiotopic selectivity of adaptation-based compression of event duration
No full textA. Bruno, I. Ayhan, and A. Johnston (2010) have recently challenged our report of spatiotopic selectivity for adaptation of event time (D. Burr, A. Tozzi, & M. C. Morrone, 2007) and also our claim that retinotopic adaptation of event time depends on perceived speed. To assist the reader judge this issue, we present here a mass of data accumulated in our laboratories over the last few years, all confirming our original conclusions. We also point out that where Bruno et al. made experimental measurements (rather than relying on theoretical reasoning), they too find clearly significant spatiotopically tuned adaptation-based compression of event time but of lower magnitude to ours. We speculate on the reasons for the differences in magnitude
The role of neural oscillations in visuo-motor communication at the time of saccades
No full textSaccadic eye-movements are fundamental for active vision, allowing observers to purposefully scan the environment with the high-resolution fovea. In this brief perspective we outline a series of experiments from our laboratories investigating the role of eye-movements and their consequences to active perception. We show that saccades lead to suppression of visual sensitivity at saccadic onset, and that this suppression is accompanied by endogenous neural oscillations in the delta range. Similar oscillations are initiated by purposeful hand movements, which lead to measurable changes in responsivity in area V1, and in the connectivity with motor area M1. Saccades also lead to clear distortions in apparent position, but only for verbal reports, not when participants respond with rapid pointing, consistent with the action of two separate visual systems in neurotypical adults. At the time of saccades, serial dependence, the positive influence on perception of previous stimulus attributes (such as orientation) is particularly strong. Again, these processes are accompanied by neural oscillations, in the alpha and low beta range. In general, oscillations seem to be tightly linked to serial dependence in perception, both in auditory judgments (around 10 Hz), and for visual judgements of face gender (14 Hz for female, 17 Hz for male). Taken together, the studies show that neural oscillations play a fundamental role in dynamic, active vision
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