Olivier Penacchio

• PhD
• University of St Andrews

While it is easy for human observers to judge an image as beautiful or ugly, aesthetic decisions result from a combination of entangled perceptual and cognitive (semantic) factors, making the understanding of aesthetic judgements particularly challenging from a scientific point of view. Furthermore, our research shows a prevailing bias in current d...

In this review, we relate theoretical work on the importance of surprise in cognition to empirical research relevant to surprise in predator–prey interactions. There have been multiple proposals as to how surprise should be defined and quantified in the context of animal cognition, including contributions from associative learning, information theo...

Binz et al. propose meta-learning as a promising avenue for modelling human cognition. They provide an in-depth reflection on the advantages of meta-learning over other computational models of cognition, including a sound discussion on how their proposal can accommodate neuroscientific insights. We argue that active inference presents similar compu...

The visual memorability of natural warning patterns: insights from humans and machines Federico De Filippi1 (fdf1@st-andrews.ac.uk), Olivier Penacchio1,2, Akira R. O'Connor1, Julie M. Harris1; 1University of St Andrews, St Andrews, United Kingdom, 2Computer Vision Center, Universitat Autònoma de Barcelona, Barcelona, Spain While some animals camo...

Inclusive design does not stop at removing physical obstacles such as staircases. It also involves identifying architectural features that impose sensory burdens, such as repetitive visual patterns that are known to potentially cause dizziness or visual discomfort. In order to assess their influence on human gait and its stability, three repetitive...

Animal warning signals show remarkable diversity, yet subjectively appear to share certain visual features that make defended prey stand out and look different from more cryptic palatable species. For example, many (but far from all) warning signals involve high contrast elements, such as stripes and spots, and often involve the colours yellow and...

Much of the neural machinery of the early visual cortex, from the extraction of local orientations to contextual modulations through lateral interactions, is thought to have developed to provide a sparse encoding of contour in natural scenes, allowing the brain to process efficiently most of the visual scenes we are exposed to. Certain visual stimu...

Prey seldom rely on a single type of antipredator defence, often using multiple defences to avoid predation. In many cases, selection in different contexts may favour the evolution of multiple defences in a prey. However, a prey may use multiple defences to protect itself during a single predator encounter. Such “defence portfolios” that defend pre...

Preference for curvature, the curvature effect, seems to transcend cultures, species, and stimulus kinds. However, its nature and psychological mechanisms remain obscure because studies often overlook the complexity of contour characterization and disregard personal and contextual factors. To investigate the curvature effect, we propose a continuou...

Multifarious sources of selection shape visual signals and can produce phenotypic divergence. Theory predicts that variance in warning signals should be minimal due to purifying selection, yet polymorphism is abundant. While in some instances divergent signals can evolve into discrete morphs, continuously variable phenotypes are also encountered in...

Preference for curvature, the curvature effect, seems to transcend cultures, species and stimulus kinds. However, its nature and psychological mechanisms remain obscure because studies often overlook the complexity of contour characterisation and disregard personal and contextual factors. To investigate the curvature effect, we propose a continuous...

Visual discomfort is related to the statistical regularity of visual images. The contribution of luminance contrast to visual discomfort is well understood and can be framed in terms of a theory of efficient coding of natural stimuli, and linked to metabolic demand. While color is important in our interaction with nature, the effect of color on vis...

Visual discomfort is related to the statistical regularity of visual images. The contribution of luminance contrast to visual discomfort is well understood and can be framed in terms of a theory of efficient coding of natural stimuli, and linked to metabolic demand. While color is important in our interaction with nature, the effect of color on vis...

Here, we investigate the camouflage consequences of animal orientation behaviour. Shadows can be a conspicuous cue to the presence of prey. For bilaterally symmetrical animals, light field modelling indicates that camouflage will be improved when an animal orients its longitudinal axis directly towards or away from the sun, because the appearance o...

Sensory stimuli can induce seizures in patients with epilepsy and predisposed subjects. Visual stimuli are the most common triggers, provoking seizures through an abnormal response to light or pattern. Sensitive patients may intentionally provoke their seizures through visual stimuli. Self-induction methods are widely described in photo-sensitive p...

The human visual system is not a colorimeter. The perceived colour of a region does not only depend on its colour spectrum, but also on the colour spectra and geometric arrangement of neighbouring regions, a phenomenon called chromatic induction. Chromatic induction is thought to be driven by lateral interactions: the activity of a central neuron i...

Animal warning signals show remarkable diversity, yet subjectively appear to share visual features that make defended prey stand out and look different from more cryptic palatable species. Here we develop and apply a computational model that emulates avian visual processing of pattern and colour to Lepidopteran wing patterns to show that warning si...

Background: Images that deviate from natural scene statistics in terms of spatial frequency and orientation content can produce visual stress (also known as visual discomfort), especially for migraine sufferers. These images appear to over-activate the visual cortex. Objective: To connect the literature on visual discomfort with a common chronic...

An apparent and common feature of aposematic patterns is that they contain a high level of achromatic (luminance) contrast, for example, many warning signals combine black spots and stripes with a lighter colour such as yellow. However, the potential importance of achromatic contrast, as distinct from colour contrast, in reducing predation has been...

1. The speed with which text can be read is determined in part by the spatial regularity and similarity of vertical letter strokes as assessed by the height of the first peak in the horizontal autocorrelation of the text. The height of this peak was determined for two passages in 20 fonts. The peak was unaffected by the size of the text or its cont...

The speed with which text can be read is determined in part by the spatial regularity and similarity of vertical letter strokes as assessed by the height of the first peak in the horizontal autocorrelation of the text. The height of this peak was determined for two passages in 20 fonts. The peak was unaffected by the size of the text or its content...

Can curvature drive preference, perceived familiarity, complexity, stability and approachability for architectural façades? In this study, we generated four versions of the same reference building, varying only the amount of curvature introduced in the façade. Participants’ judgments were measured using three experimental methodologies. Multidimens...

Visual patterns are all around us. Despite overwhelming evidence from the visual sciences that some visual patterns, in particular highly-geometric and repetitive patterns, can be aversive, patterns in our visual environment are rarely considered with regard to their impact on brain, behaviour and well-being. Yet, attempts toward developing healthi...

Countershading is a pattern of coloration thought to have evolved in order to implement camouflage. By adopting a pattern of coloration that makes the surface facing towards the sun darker and the surface facing away from the sun lighter, the overall amount of light reflected off an animal can be made more uniformly bright. Countershading could hen...

Countershading is a ubiquitous patterning of animals whereby the side that typically faces the highest illumination is darker. When tuned to specific lighting conditions and body orientation with respect to the light field, countershading minimizes the gradient of light the body reflects by counterbalancing shadowing due to illumination, and has th...

Scenes from nature share in common certain statistical properties. Images with these properties can be processed efficiently by the human brain. Patterns with unnatural statistical properties are uncomfortable to look at, and are processed inefficiently, according to computational models of the visual cortex. Consistent with such putative computati...

Significance Because the sun and sky are above us, natural illumination is directional and the cues from shading reveal shape and depth. However, many animals are darker on their backs and, over 100 years ago, it was proposed that this phenomenon was camouflage: countering the cues to shape that directional illumination creates. However, does this...

Countershading (darker coloration on the part of the body exposed to a greater light intensity) is widespread in the animal kingdom and has received constant attention by evolutionary biologists since the 19th century. It may serve several different functions, camouflage being one. Here, the gradient of coloration on the body compensates the gradie...

One of the most widespread patterns of colouration in the animal kingdom is countershading, a gradation of colour in which body parts that face a higher light intensity are darker. Countershading may help counterbalance the shadowing created by directional light, and, hence, reduce 3D object recognition via shape-from-shading. There is evidence tha...

LaySummary

Appendix S1. Independence of the results on the choice of reference orientation. Appendix S2. Compatibility of the three selective pressures for animals limited to horizontal orientations. Appendix S3. Studies showing non‐random orientation with respect to the sun.

Many animals have a gradation of body color, termed “countershading,” where the areas that are typically exposed to more light are darker. One hypothesis is that this patterning enhances visual camouflage by making the retinal image of the animal match that of the background, a fundamentally two-dimensional theory. More controversially, countershad...

Orientation with respect to the sun has been observed in a wide range of species and has generally been interpreted in terms of thermoregulation and/or ultraviolet (UV) protection. For countershaded animals, orientation with respect to the sun may also result from the pressure to exploit the gradient of coloration optimally to enhance crypsis. Here...

Quite independently of what they represent, some images provoke discomfort, and even headaches and seizures in susceptible individuals. The visual system has adapted to efficiently process the images it typically experiences, and in nature these images are usually scale-invariant. In this work, we sought to characterize the images responsible for d...

Watching a subtitled programme is a complex activity, as it entails paying attention to various stimuli simultaneously, some of which are visual (images and subtitles) and others auditory (oral language and background sounds). The aim of this study is to analyse the ocular movement of a group of children including both hearing and deaf children whe...

Animal camouflage is a paradigmatic example of evolution by natural selection, and can only be understood in terms of adaptation to deceive the brains of potential predators and to the environment. Counter-shading is a very common pattern of coloration in the animal kingdom. Countershaded animals are darker on the side that faces a greater light in...

Intrinsic characterization of scenes is often the best way to overcome the illumination variability artifacts that complicate most computer vision problems, from 3D reconstruction to object or material recognition. This paper examines the deficiency of existing intrinsic image models to accurately account for the effects of illuminant color and sen...

Download full paper at: http://www.cg.informatik.uni-siegen.de/en/shida/ Scene decomposition into its illuminant, shading, and reflectance intrinsic images is an essential step for scene understanding. Collecting intrinsic image groundtruth data is a laborious task. The assumptions on which the ground-truth procedures are based limit their applica...

Brightness induction is the modulation of the perceived intensity of an area by the luminance of surrounding areas. Recent neurophysiological evidence suggests that brightness information might be explicitly represented in V1, in contrast to the more common assumption that the striate cortex is an area mostly responsive to sensory information. Here...

Supplementary Material. Neurodynamical model of contextual influences mediated by intra-cortical interactions in V1 (following [35]). Proposed model parameters. (PDF)

Supplementary Material. Supplementary results (Figure S1 in Text S3 and Figure S2 in Text S3). (PDF)

Supplementary Material. Wavelet analysis. (PDF)

Supplementary Material. Frequency gain of the model (Figure S3 in Text S4). (PDF)

A significative percentage of the human population suffer from impairments in their capacity to distinguish or even see colours. For them, everyday tasks like navigating through a train or metro network map becomes demanding. We present a novel technique for extracting colour information from everyday natural stimuli and presenting it to visually im...

Background / Purpose: We aimed to reproduce brightness induction by using a neurodynamical model of V1 that considers contextual influences. Main conclusion: Both brightness induction and visual saliency can be modeled by a common neurodynamical architecture.

In the last years, intrinsic image decomposition has gained attention. Most of the state-of-the-art methods are based on the assumption that reflectance changes come along with strong image edges. Recently, user intervention in the recovery problem has proved to be a remarkable source of improvement. In this paper, we propose a novel approach that...

We describe an equivalence of categories between the category of mixed Hodge structures and a category of equivariant vector bundles on a toric model of the complex projective plane which verify some semistability condition. We then apply this correspondence to define an invariant which generalizes the notion of R-split mixed Hodge structure and gi...