This thesis presents the design of a tactile device that can be used to display varying magnitudes of roughness. The device is designed to be attached to an existing force feedback device in order to create a package that is able to display both macro-level (force feedback) and micro-level (tactile feedback) information to the users. This device allows the users to feel a simulated texture by placing an index finger on an aperture. The stimulus is created with a spiral brush made of nylon bristles. The brush is attached to a DC motor and the speed and direction of rotation of the brush are used to generate textures at the fingertip through the aperture. Three psychophysical experiments are conducted to study the effects of speed and direction on the roughness perception. The first experiment is designed to investigate the sensitivity to a change in the speed of the brush. This experiment is conducted for two levels of base speed and it is found that as the base speed increases, the just noticeable difference (JND) with respect to speed decreases. In the second experiment, it is found that this tactile device is able to represent textures of rough nature, such as sandpaper. It is also found that the human roughness perception cannot be described in a unique manner. Two opposite definitions of rough textures are identified in this experiment. While some users relate an increase in the speed of the brush to increasing roughness, others relate it to decreasing roughness. Further, the results show that the effects of direction are insignificant on the roughness perception for both groups of users. In the third experiment, the effects of direction are studied more closely by presenting the two directions successively with a time gap of $0.5s$. It is found that with this small time gap, the users are able to discriminate between directions, unlike in the previous experiment. The roughness perception is affected by the change in direction when the time gap is small. These findings open further areas that need to be investigated before a robust tactile device can be designed.

The use of grading scales is common in clinical practice and research settings. A number of grading scales are available to the practitioner, however, despite their frequent use, they are only poorly understood and may be criticised for a number of things such as the variability of the assessments or the inequality of scale steps within or between scales. Hence, the global aim of this thesis was to study the McMonnies/Chapman-Davies (MC-D), Institute for Eye Research (IER), Efron, and validated bulbar redness (VBR) grading scales in order to (1) get a better understanding and (2) attempt a cross-calibration of the scales. After verifying the accuracy and precision of the objective and subjective techniques to be used (chapter 3), a series of experiments was conducted. The specific aims of this thesis were as follows: • Chapter 4: To use physical attributes of redness to determine the accuracy of the four bulbar redness grading scales. • Chapter 5: To use psychophysical scaling to estimate the perceived redness of the four bulbar redness grading scales. • Chapter 6: To investigate the effect of using reference anchors when scaling the grading scale images, and to convert grades between scales. • Chapter 7: To grade bulbar redness using cross-calibrated versions of the MC-D, IER, Efron, and VBR grading scales. Methods: • Chapter 4: Two image processing metrics, fractal dimension (D) and % pixel coverage (% PC), as well as photometric chromaticity (u’) were selected as physical measures to describe and compare redness in the four bulbar redness grading scales. Pearson correlation coefficients were calculated between each set of image metrics and the reference image grades to determine the accuracy of the scales. • Chapter 5: Ten naïve observers were asked to arrange printed copies of modified versions of the reference images (showing vascular detail only) across a distance of 1.5m for which only start and end point were indicated by 0 and 100, respectively (non-anchored scaling). After completion of scaling, the position of each image was hypothesised to reflect its perceived bulbar redness. The averaged perceived redness (across observers) for each image was used for comparison to the physical attributes of redness as determined in chapter 4. • Chapter 6: The experimental setup from chapter 5 was modified by providing the reference images of the VBR scale as additional, unlabelled anchors for psychophysical scaling (anchored scaling). Averaged perceived redness from anchored scaling was compared to non-anchored scaling, and perceived redness from anchored scaling was used to cross-calibrate grades between scales. • Chapter 7: The modified reference images of each grading scale were positioned within the 0 to 100 range according to their averaged perceived redness from anchored scaling, one scale at a time. The same 10 observers who had participated in the scaling experiments were asked to represent perceived bulbar redness of 16 sample images by placing them, one at a time, relative to the reference images of each scale. Perceived redness was taken as the measured position of the placed image from 0 and was averaged across observers. Results: • Chapter 4: Correlations were high between reference image grades and all sets of objective metrics (all Pearson’s r’s≥0.88, p≤0.05); each physical attribute pointed to a different scale as being most accurate. Independent of the physical attribute used, there were wide discrepancies between scale grades, with sometimes little overlap of equivalent levels when comparing the scales. • Chapter 5: The perceived redness of the reference images within each scale was ordered as expected, but not all consecutive within-scale levels were rated as having different redness. Perceived redness of the reference images varied between scales, with different ranges of severity being covered by the images. The perceived redness was strongly associated with the physical attributes of the reference images. • Chapter 6: There were differences in perceived redness range and when comparing reference levels between scales. Anchored scaling resulted in an apparent shift to lower perceived redness for all but one reference image compared to non-anchored scaling, with the rank order of the 20 images for both procedures remaining fairly constant (Spearman’s ρ=0.99). • Chapter 7: Overall, perceived redness depended on the sample image and the reference scale used (RM ANOVA; p=0.0008); 6 of the 16 images had a perceived redness that was significantly different between at least two of the scales. Between-scale correlation coefficients of concordance (CCC) ranged from 0.93 (IER vs. Efron) to 0.98 (VBR vs. Efron). Between-scale coefficients of repeatability (COR) ranged from 5 units (IER vs. VBR) to 8 units (IER vs. Efron) for the 0 to 100 range. Conclusions: • Chapter 4: Despite the generally strong linear associations between the physical characteristics of reference images in each scale, the scales themselves are not inherently accurate and are too different to allow for cross-calibration based on physical redness attributes. • Chapter 5: Subjective estimates of redness are based on a combination of chromaticity and vessel-based components. Psychophysical scaling of perceived redness lends itself to being used to cross calibrate the four clinical scales. • Chapter 6: The re-scaling of the reference images with anchored scaling suggests that redness was assessed based on within-scale characteristics and not using absolute redness scores, a mechanism that may be referred to as clinical scale constancy. The perceived redness data allow practitioners to modify the grades of the scale they commonly use so that comparisons of grading estimates between calibrated scales may be made. • Chapter 7: The use of the newly calibrated reference grades showed close agreement between grading estimates of all scales. The between-scale variability was similar to the variability typically observed when a single scale is repeatedly used. Perceived redness appears to be dependent upon the dynamic range of the reference images of the scale. In conclusion, this research showed that there are physical and perceptual differences between the reference images of all scales. A cross-calibration of the scales based on the perceived redness of the reference images provides practitioners with an opportunity to compare grades across scales, which is of particular value in research settings or if the same patient is seen by multiple practitioners who are familiar with using different scales.

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The visual cortex of human observers changes its functionality in response to visual deprivation (Boroojerdi et al., 2000). Behavioral studies have recently documented enhanced tactile abilities following a short period of visual deprivation (Facchini & Aglioti, 2003; Weisser, Stilla, Peltier, Hu, & Sathian, 2005). The current study investigated the effects of visual deprivation on two unique tactile tasks. While Facchini and Aglioti observed significant effects of visual deprivation, neither Wong, Hackeman, Hurd, and Goldreich (2011) nor Merabet et al. (2008) observed these effects. Corroborating these more recent results, no difference in grating orientation discrimination performance was observed between the sighted and visually deprived participants in the first experiment. A significant effect of experience was seen in both groups, however, irrespective of the deprivation period of 90 minutes. The second experiment immediately followed the conclusion of the first experiment. Using the same stimuli and procedures from past experiments (Norman, Clayton, Norman, & Crabtree, 2008), it investigated the participants’ haptic discrimination of 3-dimensional object shape. Again, no significant difference in performance was found between the sighted and visually deprived participants. Together, the current results show that a brief period of visual deprivation (1.5 hours) produces no significant behavioral changes for these tactile and haptic tasks.

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Visual information about the form of an object and its movement in the world can be processed independently. These processing streams must be combined, since our visual experience is of a unitary stream of information. Studies of interactions between motion and form processing can therefore provide insight into how this combination occurs. The present thesis explored two such interactions between motion and spatial coding in human vision. The title of the thesis, “Pencils and Erasers”, serves as an analogy for the thesis’ principal findings. I investigate one situation in which moving patterns can impair the visibility of stationary forms, and another in which the visibility of form is enhanced by motion. In motion-induced blindness (MIB; Bonneh, Cooperman, & Sagi, 2001), salient stationary objects can seem to disappear intermittently from awareness when surrounded by moving features. Static forms proximate to motion can be “erased” from awareness. The thesis contributes to the answer to a simple question: why does MIB happen? My interpretation of this phenomenon emphasises the possible functional benefit of such an eraser around moving form: to suppress artifacts of visual processing from awareness. Chapter 2 demonstrates that motion per se is not required for MIB (Wallis & Arnold, 2008). MIB depends on the rate of luminance change over time, rather than the velocity (or change in position) of the inducing mask. MIB can therefore be characterised as a temporal inhibition, which does not critically depend on direction selective (motion) mechanisms. A similar mechanism of temporal inhibition that does not depend on motion is that which suppresses motion streaks from awareness. The human visual system integrates information over time. Consequently, moving image features produce smeared signals, or “motion streaks”, much like photographing a moving object using a slow shutter speed. We do not experience motion streaks as much as might be expected as they are suppressed from awareness in most circumstances. Evidence suggests that this suppression is enacted by a process of local temporal inhibition, and does not depend on motion mechanisms – much like MIB. These similarities led us to propose that MIB and motion streak suppression might reflect the same mechanism. In the case of MIB, physically present static targets may not be differentiated from signals arising from within the visual system, such as a motion streak. Chapter 3 of the thesis presents four converging lines of evidence in support of this hypothesis (Wallis & Arnold, 2009). The link between MIB and a mechanism of temporal inhibition that serves to suppress motion streaks is further strengthened by a recent report from our laboratory of a new visual illusion, Spatio-Temporal Rivalry (STR; Arnold, Erskine, Roseboom, & Wallis, in press), that is included in the present thesis as an appendix. Why does MIB occur? I suggest that at its base level, MIB reflects the activity of this simple visual mechanism of temporal inhibition (see Gorea & Caetta, 2009). This mechanism might usually serve a functional role in everyday vision: for example, by suppressing the perception of motion streaks. The second motion and form interaction investigated in the thesis represents a situation in which motion can improve form sensitivity. In some situations, observing a moving pattern can objectively improve sensitivity to that pattern after the offset of motion. The visual system can “pencil in”, or improve the visibility of, subsequent visual input. When a form defined by its motion relative to the background ceases to move, it does not seem to instantly disappear. Instead, the form is perceived to remain segregated from the background for a short period, before slowly fading. It is possible that this percept represents a consequence of bias or expectation, not a modulation of static form visibility by motion. Contrary to this possibility, Wallis, Williams and Arnold (2009) demonstrate that alignment sensitivity to spatial forms is improved by pre-exposure to moving forms (Chapter 4). I suggest that the subjective persistence of forms after motion offset and this spatial facilitation may represent two consequences of the same signal. The experiments herein address one situation in which moving patterns can impair the visibility of stationary forms and one in which moving patterns enhance the visibility of stationary forms. Therefore, the present thesis characterises two interactions between form and motion processing in human vision. These mechanisms of “pencil” and “eraser” facilitate the clear perception of objects in our visual world.

The spatial frequency doubling illusion (FDI) occurs when the contrast of a low spatial frequency sinusoidal grating is modulated at high temporal frequencies – its apparent spatial frequency increases. Earlier suggestions were that the FDI is generated by a specific class of retinal ganglion cells, which are preferentially lost in the early stages of glaucoma. Based on this linking theory, frequency doubling perimetry (FDP) was developed and several clinical reports confirmed its high efficiency in diagnosing early glaucomatous vision loss. However, this linking theory is not universally accepted and newer suggestions posit that the illusion arises because of temporal frequency related difficulties in temporal phase encoding ability. This thesis psychophysically examines the spatiotemporal characteristics of both the FDI and temporal phase encoding ability with achromatic and equi-luminant (both red-green (RG) and blue-yellow (BY)) gratings at a range of spatiotemporal parameters including those eliciting the FDI. (For complete abstract open document)

Thesis (M.A.)--Carleton University, 2004. / Includes bibliographical references (p. 73-77). Also available in electronic format on the Internet.

Le but de cette thèse est de proposer des méthodes pour pouvoir évaluer les performances durant la lecture sur support électronique, afin de pouvoir comparer plusieurs dispositifs d’affichage. Des tests permettant d’effectuer des mesures de performances de manière répétée ont été construits pour chacune des dimensions classiques de la lecture électronique : visibilité (test de caractérisation psychométrique), lisibilité (identification de lettres, décision lexicale, vitesse de lecture de phrases générées automatiquement) et compréhension (mesure de la mémorisation et des inférences pendant la lecture de textes générés automatiquement). Au-delà de ces dimensions classiques, nous avons réalisé deux études pour examiner le lien entre la lecture sur support électronique et la posture des utilisateurs. La première montre qu’une posture pouvant être engendrée par l’utilisation de tablette (inclinaison latérale de tête) n’affecte pas la performance de lecture. La seconde étude posturale montre l’effet de la difficulté d’un texte sur la distance à l’écran pendant l’utilisation d’une liseuse électronique ; les sujets se rapprochent de l’écran lorsque leur niveau d’attention augmente. L’ensemble des tests développés et une mesure de posture ont été regroupés dans une batterie de tests visant à quantifier la performance de lecture associée à un support donné ; l’indicateur résultant étant appelé « Quotient de Lecture Electronique ». Cet indicateur a été calculé pour un écran d’ordinateur, un vidéoprojecteur et une tablette. Les résultats expérimentaux montrent que les tests permettent de comparer les supports, notamment en termes de visibilité et de lisibilité. / The aim of this thesis is to offer methods of evaluating performance during digital reading, in order to be able to compare different display devices. Tests were developed allowing repeated measurements for classic measures of digital reading: visibility (psychometric characterization), readability (letter identification, lexical decision, reading speed on automatically generated sentences) and comprehension (memorization and inference measurement while reading automatically generated texts). Beyond these classic dimensions, we also conducted two studies in order to examine the link between digital reading and the posture adopted by the device users. The first revealed that a tablet-use-related posture (lateral head tilt) does not affect reading performance. The second postural study demonstrated the effect of text difficulty on eye-screen distance during the use of an e-reader. Subjects approached the screen as their attentional level increased. The constructed tests and a postural measure were aggregated into a battery of tests permitting the evaluation of reading performance associated with a device. The resulting indicator is called the “Digital Reading Quotient”. This indicator has been computed for a computer screen, a projector and a tablet. The experimental results show that these tests can be used in order to compare different devices, especially in terms of visibility and readability.