3,565 research outputs found
Il paesaggio agro-zootecnico e silvo-pastorale della montagna alpina
No full textIl paesaggio, inteso come il risultato dell’interazione fra le esigenze e le attività della società umana e le opportunità e i vincoli che il territorio offre e pone a esse con le sue componenti naturali abiotiche e biotiche, è in continua, inevitabile evoluzione. Se da un lato non può, pertanto, essere imbalsamato, dall’altro è necessario che la sua evoluzione sia indirizzata positivamente, comprendendo il ruolo esercitato dalle varie attività umane e orientandole opportunamente. E’ in tale prospettiva che questo testo affronta il rapporto fra zootecnia e paesaggio. Ampie zone rurali del Paese sono, infatti, caratterizzate da condizioni morfologiche e climatiche che le rendono idonee, più che all’agricoltura, all’allevamento, su cui si sono conseguenza improntati moduli architettonici, modelli culturali e metodi di utilizzo delle superfici agro-forestali che hanno creato veri e propri “paesaggi zootecnici”.
Maurizio Ramanzin e Luca Battaglini considerano il paesaggio alpino, esaminando come scenari alternativi di evoluzione dei sistemi zootecnici che l’hanno modellato potrebbero influenzare i beni e servizi che esso offre alla società, partendo dalla produzione di alimenti di elevata qualità, passando per il contributo alla protezione dai dissesti e alla conservazione della biodiversità, e terminando con la valorizzazione culturale ed estetico-ricreativa
Ocular dominance for optical-visual correction, strategies and clarifications
No full textopenCon questo progetto di tesi si è voluto cercare, per quanto ampio e variegato sia l’argomento, di fornire e approfondire le nozioni sulla dominanza oculare, di descrivere alcune strategie e fare alcune precisazioni.
Importante è stato capire il ruolo della dominanza oculare in ambito optometrico e non, quindi la sua utilità per i vari metodi compensativi e la sua influenza sulla scelta di quest’ultimi.
In conclusione si è voluto presentare anche un breve accenno in riferimento alla chirurgia refrattiva.
L’elaborato comincia con un breve incipit sull’apparato oculare per poi affrontare il tema sulla dominanza oculare avendola relazionata con alcuni cenni sulla neuroanatomia del sistema visivo, in cui si è fatto riferimento alle diverse vie ottiche connesse alla componente cerebrale deputata alla visione.
Si è poi entrati nello specifico con una apposita panoramica sia sulla dominanza motoria sia sulla dominanza sensoriale con i relativi (molteplici) test per la rilevazione di entrambe.
Si è posta l’attenzione nell’analisi delle possibili analogie e differenze che si celano dietro queste due tipologie di dominanze, le caratteristiche di ognuna e dopo essersi serviti delle nozioni presenti in letteratura si è osservato e compreso se l’occhio dominante motorio coincide con quello sensoriale oppure no, e ancora, se esistono casi in cui si verifichi una alternanza della dominanza tra i due occhi o addirittura una sua totale assenza.
In questo progetto si è testato, a livello sperimentale su un campione di 15 partecipanti, l’efficacia dei test (test del foro e adattamento all’annebbiamento) con cui si rilevano le dominanze oculari ma soprattutto per vedere se i dati trovati in letteratura coincidono effettivamente con quelli del campione in esame; ed osservare quindi ancora una volta se le dominanze coesistono per un unico occhio oppure se presenti disparatamente nei due occhi (OD e OS)
Contribution of Visuospatial and Motion-Tracking to Invisible Motion
No full textPeople experience an object’s motion even when it is occluded. We investigate the processing of invisible motion in three experiments. Observers saw a moving circle passing behind an invisible, irregular hendecagonal polygon and had to respond as quickly as possible when the target had just reappeared from behind the occluder. Without explicit cues allowing the end of each of the eight hidden trajectories to be predicted (length ranging between 4.7 and 5 deg), we found as expected, if visuospatial attention was involved, anticipation errors, providing that information on pre-occluder motion was available. This indicates that the observers, rather than simply responding when they saw the target, tended to anticipate its reappearance (Experiment 1). The new finding is that, with a fixation mark indicating the centre of the invisible trajectory, a linear relationship between the physical and judged occlusion duration is found, but not without it (Experiment 2) or with a fixation mark varying in position from trial to trial (Experiment 3). We interpret the role of central fixation in the differences in distinguishing trajectories smaller than 0.3 deg, by suggesting that it reflects spatiotemporal computation and motion-tracking. These two mechanisms allow visual imagery to form of the point symmetrical to that of the disappearance, with respect to fixation, and then for the occluded moving target to be tracked up to this point
Suppressive effects on motion discrimination induced by transient flankers are reduced by perceptual learning
No full textWe investigated spatial suppression of a drifting Gabor
target of 0.5 c/8 induced by adjacent and iso-oriented
stationary Gabors (flankers) whose spatial frequency
differed by 61 and 62 octaves to that of the drifting
target. Stimuli (target and flankers) were presented for
33 ms. Results showed greater spatial suppression
when the spatial frequency of the stationary but
transient flanking Gabors was either equal or 1–2
octaves lower than when it was 1–2 octaves higher
than the target’s spatial frequency. This asymmetry
was evident only for the drifting target, but not for
the stationary target. In addition, we investigated
whether perceptual learning (PL) reduced the spatial
suppression induced by the flankers. We found that PL
increased contrast sensitivity for the target, but only
when it was reduced by the lateral masking flankers,
and its effect did not transfer to an isolated drifting
target of equal or higher spatial frequency. These
results suggest that PL selectively affects suppressive
interactions rather than contrast gain. We suggest that
the suppressive effect of low spatial frequency
flankers and the lack of suppression with high spatial
frequency flankers may reflect two complementary
phenomena: camouflage by the transient flankers (i.e.,
context) and breaking of camouflage by form-motion
segmentation. Camouflage may result because both
target and flankers activate the motion
(magnocellular) system. Breaking of camouflage
instead may occur when target and flankers’ spatial
frequency are more suitable for quasi-independent activation of the form system (by the flankers) and the
motion system (by the target)
The extrapolation of occluded motion: basic mechanism and application
No full textPredicting the future states of moving objects that are hidden by an occluder for a brief period is of paramount importance to our ability to interact within a dynamic environment. This phenomenon is known as motion extrapolation (ME). Numerous gaps in the literature can be found disregarding the mechanisms involved in ME of which the current thesis attempts to address. Behavioural experiments usually utilize a prediction-of-motion paradigm, which requires participants to make a direct estimation of the time-to-contact (TTC). In this task, the initial trajectory of a target stimulus is presented, which then becomes occluded, observers are then asked to respond when they believe the target has reached a marked point behind that occluder without it ever actually reappearing (Tresilian, 1999; Rosenbaum, 1972). Alternatively, other experiments have adopted a timing discrimination task in which participants are required to indicate whether a moving target, following occlusion, reappears ‘early’ or ‘late’ (Makin, Poliakoff & El-Deredy, 2009; Makin, Poliakoff, Ackerley & El-Deredy, 2012).
Experiments
In the first part of this thesis, I investigated whether the visual memory system is active during the extrapolation of occluded motion and whether it reflects speed misperception due to the well-known illusion such as the apparent slower speed of low contrast object or large size object (Thompson 1982; Epstein 1978). Results revealed that with a TTC task observers estimate longer time to contact with low contrast and large stimuli compared to high contrast and small stimuli respectively. Note that the stimuli in both conditions are moving at equal speed. Therefore, the illusion of the apparent slower speed with low contrast and large stimuli remains in the visual memory system and influences motion extrapolation.
Chapter III aims to investigate the interaction between real motion and motion extrapolation. Gilden and colleagues (1995) showed that motion adaptation affects TTC judgment showing that real motion detectors are somehow also involved during ME. A step further that I made was to investigate the effect of brief motion priming and adaptation, occurring at the earliest levels of the cortical visual streams, on time-to-contact (TTC) estimation of a target passing behind an occluder. By using different exposure times of directional motion presented in the occluder area prior to the target’s disappearance behind it, my aim was to modulate (prime or adapt) extrapolated motion of the invisible target, thus producing different TTC estimates. Results showed that longer (yet sub-second) exposures to motion in the same direction of the target produced late TTC estimates, whereas shorter exposures produced shorter TTC estimates, indicating that rapid forms of motion adaptation and motion priming affect extrapolated motion. My findings suggest that motion extrapolation might occur at the earliest levels of cortical processing of motion, where these rapid mechanisms of priming and adaptation take place.
In Chapter IV of my thesis, I explore not only the visual factors of motion extrapolation, but also the timing mechanisms involved and their electrophysiological correlates. The first question is whether the temporal processing is required for accurate ME, and whether this is indexed by neural activity of the Contingent Negative Variation (CNV). A second question is, whether there is a specific electrophysiological correlates that highlight the shifting from real motion perception to motion extrapolation. In this electroencephalographic experiment, participants were adapted with a moving texture (Gilden et al., 1995). The adaptation with the moving texture could bias and modify temporal processing. Participants made a direct estimation of Time to Contact, which showed that classic adaptations were able to bias temporal judgments and modulate the amplitude of the CNV, suggesting a complex feedforward-feedback network between low- and high level cortical mechanisms. Finally, a negative defection (N190) was found, for the first time, as a neurophysiological correlate in the temporal-occipital electrodes in the right and left hemisphere for the rightwards and leftwards ME respectively, indicating the involvement of motion mechanisms of intermediate cortical level in ME.
Chapter V aims to show at distinguishing between extrapolation, and interpolation of occluded motion. Extrapolation is the ability to extract the trajectory, speed and direction of a moving target that becomes hidden by an occluder, thanks to the information extracted from the visible trajectory. Interpolation is a similar phenomenon, i.e. from the visible trajectory one can extract speed and direction as in Extrapolation. The main difference is that for interpolate visible cue are needed along the invisible trajectory. If the occluder is invisible and the occluded trajectory is symmetrical respect to a visible cue, one can connect these cues (spatial points) in order to form a spatio-temporal map and infer where and when the target will reappear. This is not possible in absence of visible cues such as in extrapolation condition. In a new task, observers were required to press a button as fast as possible (reaction time) when they saw a moving target reappearing from an invisible occluder. Results showed that observers could even anticipate the reappearance of an object moving behind the occluder. However, only in some circumstances: i) when the occluder was not positioned over the blind spot but in retinal areas that project to the visual cortex; ii) with an entirely invisible occluder the visible motion before occlusion had to be presented and iii) visual-spatial cues had to signal the center of the invisible trajectory. When these conditions are given, observers can use the spatial information given by the point of disappearance, the visible cue that represented the center of the invisible trajectory, then infer the point of reappearance by symmetry. Therefore having a set of discrete spatial positions (and its cortical representation) in which the moving occluded target will be in a certain moment of time, it is convenient to interpolate this point in order to create a spatio-temporal map to infer where and when the object will be (saliency map). I consider this process of motion interpolation as an amodal filling-in process.
The last part of my thesis involved a practical application of ME. Participants cannot interpolate when the moving target passes in a zone over retinal areas that do not project to the visual cortex (blind spot). In this case, observers perform a true reaction time and do not anticipate the response. Patients with Macular Degeneration cannot see with their fovea since it is damaged. Therefore, that part of the retina does not project to the visual cortex anymore. In a task in which they have to press a response button when a moving target disappear into or reappear from their scotoma, we predict that they cannot anticipate the response to the reappearance of the target. Five patients with macular degeneration were therefore instructed to press a button when they see a moving target disappear into and reappear from their scotoma. Patients repeated this task several times with different linear trajectories of the target. Connecting the point in space in which a patient presses the button, it was possible to draw the shape and the size of the scotoma with a software. The size of the scomota found with this experiment was compared with that measured with a Nidek MP-1. A linear correlation of R2 about of 0.8 was found between the Nidek MP-1 and scotoma measured connecting the point in which patients reported to see the target reappear from their scotoma. Therefore, this software which was written by me (considering its limits) may become a useful tool to obtain a reliable perimetry in a given situation in which an expensive machine such as the MP-1 is not available
Illusory speed is retained in memory during invisible motion
No full textThe brain can retain speed information in early visual short-term memory in an astonishingly precise manner. We investigated whether this (early) visual memory system is active during the extrapolation of occluded motion and whether it reflects speed misperception due to contrast and size. Experiments 1A and 2A showed that reducing target contrast or increasing its size led to an illusory speed underestimation. Experiments 1B, 2B, and 3 showed that this illusory phenomenon is reflected in the memory of speed during occluded motion, independent of the range of visible speeds, of the length of the visible trajectory or the invisible trajectory, and of the type of task. These results suggest that illusory speed is retained in memory during invisible motion
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