Drawing from a still-life is a complex visuomotor task. Nevertheless, experts depict three-dimensional subjects convincingly with two-dimensional images. Drawing research has previously been limited by its general dependence on qualitative assessment of drawings by human critics and on retrospective self-report of expertise by drawers. Accuracy measures cannot hope to encompass all the properties of “goodness” in a drawing but this thesis will show that they are consistent with the expertise of the drawers and with the quality ratings of human critics, they are robust enough to support analysis of ecologically valid drawing tasks from complex three-dimensional stimuli, and they are sensitive enough to study global and local properties of drawings. Drawing expertise may depend to some extent on more accurate internal models of 3D space. To explore this possibility we had adults with a range of drawing experience draw a still life. We measured the angles at intersecting edges in the drawings to calculate each person's mean percentage magnitude error across angles in the still life. This gave a continuous objective measure of drawing accuracy which correlated well with years of art experience. Participants also made perceptual judgements of still lifes, both from direct observation and from an imagined side view. A conventional mental rotation task failed to differentiate drawing expertise. However, those who drew angles more accurately were also significantly better judges of slant, i.e., the pitch of edges in the still life. Those with the most drawing experience were significantly better judges of spatial extent, i.e., which landmarks were leftmost, rightmost, nearest, farthest etc.. The ability to visualize in three dimensions the orientation and relationships of components of a still life is related to drawing accuracy and expertise. In our second study, we set out to extend our understanding of drawing accuracy and to develop measures that would support more complex research questions about both drawing and visual perception. We developed and applied novel objective geometric measures of accuracy to analyze a perspective drawing task. We measured the deformation of shapes in drawings relative to the ground truth of a reference photograph and validated these measures by showing that they discriminate appropriately between experts and novices. On all measures—orientation, proportionality, scale and position of shapes—experts outperformed novices. However, error is not uniform across the image. Participants were better at capturing the proportions and positions of objects (the “positive space”) than of the spaces between those objects (the “negative space”) and worse at orienting those objects than shapes in the negative space, but scale error did not differ significantly between positive and negative space. We have demonstrated that objective geometric measures of drawing accuracy are consistent with expertise and that they can be applied to new levels of analysis, not merely to support the conventional wisdom of art educators but to develop new, evidence-based means of training this fundamental skill. Most or all prior research into drawing was based on human ratings of drawing quality, but we cannot take for granted that the “goodness” of a drawing is related to its accuracy. In order to determine whether our objective measures of accuracy are consistent with drawing quality, we invited more than one hundred participants to grade the quality of all of the drawings we had collected and measured. We showed participants photographs of the still lifes on which the drawings were based and asked them to grade the quality of each drawing on a scale from 1 (“Poor”) to 10 (“Excellent”). People's quality ratings were consistent with one another. People without drawing experience rated drawings slightly more highly than the drawing experts did, but the ratings of both groups correlated well. As we predicted, the more drawing experience the artist had, the more highly rated the drawing was, and the more accurate the drawing was, the more highly rated it was. Furthermore, scaling error (but not proportionality, orientation or position) also predicted drawing quality. In perspective drawing, accuracy—as measured by angle error or polygon error—is related to drawing quality. If drawing practice strengthens an artist's model of 3D space, we would expect the three-dimensionality of drawings to be disrupted by damage to the dorsal stream or the connection between the dorsal and ventral streams. A former illustrator and animator, DM, who had suffered a right hemisphere stroke and presented with spatial neglect, performed modified versions of the angle judgement, spatial judgement and indirect drawing tasks of our second study. Despite his previous experience, he showed weaknesses in his mental model of 3D space, weaknesses that were not evident in his drawings before the stroke. Taken together, the thesis has developed and validated two objective measures of drawing accuracy that both capture expert/novice differences well and provide superior measures when contrasted with self-reported expertise. The performance of a single patient with neglect highlights the potential involvement of the dorsal stream in drawing. The novel quantitative measures developed here allow for testable hypotheses concerning the cognitive and neural mechanisms that support the complex skill of drawing to be objectively measured.

Drawing from a still-life is a complex visuomotor task. Nevertheless, experts depict three-dimensional subjects convincingly with two-dimensional images. Drawing research has previously been limited by its general dependence on qualitative assessment of drawings by human critics and on retrospective self-report of expertise by drawers. Accuracy measures cannot hope to encompass all the properties of “goodness” in a drawing but this thesis will show that they are consistent with the expertise of the drawers and with the quality ratings of human critics, they are robust enough to support analysis of ecologically valid drawing tasks from complex three-dimensional stimuli, and they are sensitive enough to study global and local properties of drawings. Drawing expertise may depend to some extent on more accurate internal models of 3D space. To explore this possibility we had adults with a range of drawing experience draw a still life. We measured the angles at intersecting edges in the drawings to calculate each person's mean percentage magnitude error across angles in the still life. This gave a continuous objective measure of drawing accuracy which correlated well with years of art experience. Participants also made perceptual judgements of still lifes, both from direct observation and from an imagined side view. A conventional mental rotation task failed to differentiate drawing expertise. However, those who drew angles more accurately were also significantly better judges of slant, i.e., the pitch of edges in the still life. Those with the most drawing experience were significantly better judges of spatial extent, i.e., which landmarks were leftmost, rightmost, nearest, farthest etc.. The ability to visualize in three dimensions the orientation and relationships of components of a still life is related to drawing accuracy and expertise. In our second study, we set out to extend our understanding of drawing accuracy and to develop measures that would support more complex research questions about both drawing and visual perception. We developed and applied novel objective geometric measures of accuracy to analyze a perspective drawing task. We measured the deformation of shapes in drawings relative to the ground truth of a reference photograph and validated these measures by showing that they discriminate appropriately between experts and novices. On all measures—orientation, proportionality, scale and position of shapes—experts outperformed novices. However, error is not uniform across the image. Participants were better at capturing the proportions and positions of objects (the “positive space”) than of the spaces between those objects (the “negative space”) and worse at orienting those objects than shapes in the negative space, but scale error did not differ significantly between positive and negative space. We have demonstrated that objective geometric measures of drawing accuracy are consistent with expertise and that they can be applied to new levels of analysis, not merely to support the conventional wisdom of art educators but to develop new, evidence-based means of training this fundamental skill. Most or all prior research into drawing was based on human ratings of drawing quality, but we cannot take for granted that the “goodness” of a drawing is related to its accuracy. In order to determine whether our objective measures of accuracy are consistent with drawing quality, we invited more than one hundred participants to grade the quality of all of the drawings we had collected and measured. We showed participants photographs of the still lifes on which the drawings were based and asked them to grade the quality of each drawing on a scale from 1 (“Poor”) to 10 (“Excellent”). People's quality ratings were consistent with one another. People without drawing experience rated drawings slightly more highly than the drawing experts did, but the ratings of both groups correlated well. As we predicted, the more drawing experience the artist had, the more highly rated the drawing was, and the more accurate the drawing was, the more highly rated it was. Furthermore, scaling error (but not proportionality, orientation or position) also predicted drawing quality. In perspective drawing, accuracy—as measured by angle error or polygon error—is related to drawing quality. If drawing practice strengthens an artist's model of 3D space, we would expect the three-dimensionality of drawings to be disrupted by damage to the dorsal stream or the connection between the dorsal and ventral streams. A former illustrator and animator, DM, who had suffered a right hemisphere stroke and presented with spatial neglect, performed modified versions of the angle judgement, spatial judgement and indirect drawing tasks of our second study. Despite his previous experience, he showed weaknesses in his mental model of 3D space, weaknesses that were not evident in his drawings before the stroke. Taken together, the thesis has developed and validated two objective measures of drawing accuracy that both capture expert/novice differences well and provide superior measures when contrasted with self-reported expertise. The performance of a single patient with neglect highlights the potential involvement of the dorsal stream in drawing. The novel quantitative measures developed here allow for testable hypotheses concerning the cognitive and neural mechanisms that support the complex skill of drawing to be objectively measured.

La précision en dessin a été considérablement étudiée chez l'enfant, mais la raison pour laquelle certains adultes sont bien plus précis que d'autres à copier des objets ou des scènes demeure un mystère. Un facteur possible serait l'entrainement : les artistes passent des milliers d'heures à faire des dessins. Le but de cette thèse a été d'explorer dans quelle mesure cet entrainement intensif a pu affecter certains processus de la vision et de la mémoire visuelle. Dans une série d'études, nous avons tout d'abord démontré que l'expertise en dessin n'est pas liée à une perception plus véridique du monde. En effet, les artistes professionnels et les étudiants en Art que nous avons testé n'étaient pas davantage capables de défaire les mécanismes perceptifs automatiques qui corrigent d'ordinaire les effets dus au contexte visuel. Ils étaient autant affectés par les constances visuelles que les novices. Ceci suggère qu'un entrainement en dessin ne pourrait pas affecter des mécanismes perceptifs déjà bien établis, mais plutôt des processus de plus haut ordre, tels que l'analyse visuelle de structure d'objets. Dans deux études, nous avons ensuite cherché à déterminer comment les dessinateurs encodent et intègrent les informations structurelles lorsqu'ils analysent un objet pour le dessiner. Tout d'abord, afin de tester si les artistes avaient une meilleure représentation de formes complexes, nous avons élaboré une tâche de fenêtre contingente dans laquelle les participants devaient classer un objet comme structurellement possible ou impossible alors qu'ils ne pouvaient voir qu'une portion de l'objet centrée sur la position du regard. Les experts étaient capables de faire cette tâche avec de plus petites portions de l'objet. La compétence en dessin serait ainsi liée à la capacité d'intégrer des échantillons d'informations extraits lors de chaque fixation en une représentation interne plus robuste. Nous avons ensuite voulu savoir si la précision en dessin pouvait aussi être liée à l'efficacité de l'encodage des informations structurelles à partir d'une seule fixation (sans mouvements oculaires autorisés), avec l'objet centré soit sur la position de la fixation ou en périphérie visuelle. Nous avons trouvé que les sujets entrainés étaient capables de discriminer des objets impossibles d'objets possibles avec des durées de présentation plus courtes, que ce soit en vision centrale ou périphérique. Enfin, nous avons étudié le rôle de la mémoire visuelle pendant le processus de dessin et cherché à déterminer si les dessinateurs avaient une représentation plus précise de la position des traits de l'objet. Pour cela, nous avons développé une expérience couplant une tâche de dessin sur tablette graphique et une tâche de détection de changement durant laquelle les participants devaient copier une figure sur une tablette graphique. Tout au long du processus de copie, des changements pouvaient intervenir à la fois sur la figure originale et sur la copie, et les participants devaient corriger tout changement détecté, (la figure et le dessin n'étaient visibles qu'en alternance). Nos résultats ont montré que tous nos participants détectaient mieux les changements présents dans la figure originale que dans leur propre dessin. De plus, les experts en dessin était bien meilleurs à détecter les changements, mais seulement lorsque le dessin était impliqué (contrasté avec une simple tâche de détection de changement sans dessin). Pris ensembles, ces résultats démontrent qu'un entrainement intensif en dessin peut affecter des mécanismes perceptifs de haut niveau ainsi que des mécanismes de mémoire visuelle, et non les mécanismes perceptifs basiques déjà bien établis par la longue expérience perceptive que nous partageons tous. / Drawing accuracy has been extensively studied in children, but very little is known of what would make some adults more accurate in copying objects or scenes than many others. One factor may simply be practice: artists have often spent thousands of hours making drawings. The focus of this thesis has been to explore how this intensive practice has affected visual and memory processes. In a series of studies, we first demonstrated that drawing expertise does not relate to a more veridical perception of the world: professional artists and art students were no better than novices at seeing scenes accurately - at undoing the automatic perceptual mechanisms that ordinarily correct for visual context like shadows and depth (visual constancies). This suggests that intensive training in drawing may not affect already well-established perceptual mechanisms, but might affect higher-order processes such as visual analysis of object structure. In a number of studies, we next investigated how trained draftspersons visually encode and integrate structural information when analyzing an object. First, to test whether artists had a more advanced ability to represent complex shapes, we designed a gaze-contingent moving window task where participants had to classify an object as structurally possible or impossible, while only being able to see a portion of the object centered on the gaze position. Experts were able to perform this task with smaller samples of the object. This result suggests that skill in drawing relates to the ability to integrate local samples from each fixation into a more robust internal representation. We then asked whether drawing accuracy could also be related to the encoding efficiency of structural information from a single fixation (no eye movements allowed), with the test object centered at fixation or located in peripheral vision. In this case, we found that experts could discriminate possible vs impossible objects with shorter presentation durations and this was true whether the object was presented at fixation or in the periphery. Finally, we investigated the role of visual memory during the drawing process and whether more skilled participants have a better representation of feature locations. To do so, we designed an interactive pen tablet experiment coupled with a change detection task where participants had to copy a figure on a pen tablet. Throughout the copying process, changes could occur in both the original figure and the copy and participants had to correct any changes they noticed (the figure and the drawing were visible in alternation). We found that all participants detected changes better when they occurred in the original than in their own drawing. Moreover, experts were better at detecting changes, but only when drawing was involved (contrasted with a simple change detection task without drawing). Taken together these results demonstrate that intensive training in drawing affects higher-order perceptual and visual memory mechanisms but not basic perceptual mechanisms that already well grounded on the life-long perceptual experiences that we all share.