ISBCS 2020 – Effect of expectations on perception of dynamic material properties

Authors – Amna Malik, Katja Doerschner, Hüseyin Boyaci

The current global situation that we are all facing has forced us to look to the virtual world in order to continue within academia and research. Amna Malik, hosted by the University of Bilkent, has done just, virtually narrating her video for ISBCS presentation.

In the abstract Amna says:

“Visual information plays a vital role in object and material recognition. Based on our daily life interaction with objects, our brain learns to make associations between how an object looks like, what material it is made of and its physical and functional properties. Hence, before even we touch an object, simply by looking at it, we have expectations about how it will behave under different forces. For example, we expect a wine glass to shatter if it falls and hits the ground. Upon viewing an object, incoming visual information is combined with prior knowledge to help us recognizing objects, accessing their properties and making efficient decisions regarding actions involving interaction with objects. In this study we aimed to investigate the role of expectations in perception of material properties in dynamic scenes and how they affect perceptual decisions. We used novel computer animations of objects falling on ground, which are manipulated to behave in an expected or unexpected manner. Observers were asked to answer whether the object broke or not upon hitting the ground. We measured reaction times and percent correct responses for each condition. We found out that observers take longer to respond in the surprising condition. Hence, we concluded that expectations influence perception of dynamic material properties and perceptual decision making is delayed when these expectations are violated, which implies that additional processing is required when incoming sensory information does not match the expectations.”

We would like to congratulate Amna on a terrific presentation and encourage everyone to watch the video!

Visual Science of Art Conference 2019

Written by Jacob Cheeseman

As someone who considers himself a scientist first, and an artist second, I came to the Visual Science of Art Conference (VSAC) 2019 with keen interest. The meeting aims to enhance our scientific understanding of how visual artists depict the world, and to further communication between fields that, while traditionally divided within academia, share a passion for seeing.
This year we were gathered in Leuven, Belgium, a city that could well have the perfect balance of culture and functionality. And the opening reception was held at the Stadhuis, an absolutely gorgeous example of 15th-century gothic architecture. Our group was welcomed in this grand hall by no less than the mayor of Leuven, Mohamed Ridouani, whose presence signified how this alliance of art and science has strengthened both communities.

Stadhuis van Leuven

The content of the meeting spanned a range of diverse topics, including the visual perception of material properties, empirical aesthetics, and historical studies of rendering techniques. There was also no shortage of visual art—the work of Maaike Schoorel being a notable example. Working from reference photographs of real scenes, she paints a kind of phantasmic representation of the original image, accentuating only the critical lines and shading that suggest the underlying forms. The effect is to break any photographic constraints on interpretation, and to allow each viewer to project their own imagery onto the canvas.

Maaike Schoorel, Oranje Boterbloemen (Orange Buttercups), oil on canvas, 2011

The work I presented at the conference also deals with visual ambiguity, specifically the kind that depends on how we estimate distances in photographs. In everyday circumstances, our ability to identify surface material properties is effortless and automatic, but occasionally this ability can be challenged, especially when the visual pattern impedes a reliable estimation of distance. This can be seen in aerial photographs of planted fields, which can appear strikingly similar to woven fabric or textile. The pattern of light does not specify which interpretation is correct, and so our interpretations reveal what distances we have learned to associate with such images.

Jacob R. Cheeseman, Hunting for Ambiguity, photograph, 2018

In Jan Koenderink’s latest book, The Way of The Eye, he frames visual perception as a process of continually questioning our interpretations of images. Our first impression of what we are looking at is usually quite convincing, but if we relax our focus, other impressions enter into view. Surrealist painters like Dali seem to possess a supernatural talent for imagining multiple interpretations simultaneously, but how to compose photographs with this property strikes me as a slightly different, and perhaps more difficult task. When I asked Dr. Koenderink how one could compose such images, he suggested that it was a matter of attentional training.

To this end, I once spent a sunny afternoon in Giessen wandering around with my camera, hunting for ambiguous scenes. Although my perception of each scene was stable, by meditating on the question, “What else could this be?”, I began to see hints of possibility. By the end of that day I had hundreds of images, but not a clue whether any of them had captured what I had seen, or whether others would agree with my interpretations. One of my basic goals at VSAC was therefore to discuss this way of seeing with visual artists who play with ambiguity.

My line of questioning went something like this: “How does one compose images with multiple interpretations? While creating visual art, are you trying to reduce disparity between a mental image and a perceived image? Does one interpretation serve as the foundation for subsequent layers?” The answers I received to these questions were also rather ambiguous, which could mean that these are not the right questions, or that I am not ready for the answers. Maybe by the time this discussion resumes at next year’s meeting, I will be.

International Colour Vision Society Meeting 2019

Written by Ruben Pastilha

The International Colour Vision Society (ICVS) is an international group of physiologists, psychologists, physicists, geneticists, optometrists, ophthalmologists and visual scientists who have a research interest in the many aspects of colour vision and colour vision deficiencies.

Ruben Pastilha presenting his paper at the ICVS 2019

This years meeting was held in Riga, Latvia and I have been fortunate enough to win the runner-up Talk Prize.

I presented my paper on The Temporal Dynamics of Daylight: Speed Limits on Perception. Relatively little is known about human sensitivity to changes in illumination spectra over time. We have been interested in the temporal dynamics and speed limits of illumination change perception, in particular, for daylight changes. People are aware that outdoor illumination varies in chromaticity throughout the day, yet we don’t seem to directly perceive these changes while they occur. Using psychophysical testing with daylight metamers in an immersive illumination setting we found that, for 21 participants, the minimum detectable speed of chromaticity change is on average about 20 times larger than the fastest changes usually occurring in natural daylight. In addition, we found that changes in illumination chromaticity towards a neutral reference are hardest to detect, for non-neutral adaptation lights. This supports the notion that the brain encodes a neutral-daylight illumination prior.

Ruben presenting at ICVS 2019

World Haptics Conference 2019

Written by Muge Cavdan

World Haptics Conference 2019 (WHC) was the first major conference that I attend to in haptics. I was super excited to see all other works in my field. Since it is not only research but also applied field-oriented conference, I saw a lot of applications of the pure research.

First day of WHC 2019’s schedule is only included workshops. A total of 5 workshops held on current topics in haptics. I had a chance to attend “Softness Perception” which is directly related to my work. My supervisor Prof. Dr. Knut Drewing also had a talk entitled “Different Dimensions of Softness and Their Associated Exploratory Procedures” in this session.

Prof. Knut Drewing giving his talk about Different Dimensions of Softness and Their Associated Exploratory Procedures.

On the other days, talks, demonstrations, posters, & discussion sessions took place. There was a great environment in which you could have the opportunity to get involve in demonstrations and talk to people from different companies and universities during breaks or discussion sessions.

Demonstration session from 3rd day

All in all, throughout my Tokyo visit I got involved in a very different culture, met a lot of people from both industry and research, and most importantly learned how limitless what I can do in research. I would like to thank my supervisors Prof. Dr. Knut Drewing & Dr. Katja Doerschner for their support during my WHC 2019 paper submission and talk preparation.

ECVP 2019 ESR Abstracts

ECVP 2019 ESR Abstracts

The ECVP have now released the full abstracts of the attendees to the conference in Leuven. Below you will find the abstracts submitted by DyViTo ESRs. To see the full abstract book, including the abstracts that involve DyViTo Supervisors and friends of the project, please use this link.

Scale ambiguities in material recognition
Jacob R. Cheeseman*, Filipp Schmidt, Roland W. Fleming
Justus Liebig University Giessen

As a rule, observers can reliably identify the material properties of surfaces. Here, we investigated exceptions to this rule using a set of 87 photographs of materials (e.g., water, sand, stone, metal, wood) that appear to belong to different material classes depending on their apparent distance from the viewer. In three experiments, participants viewed each image and provided a categorical judgement of the depicted material, and a quantitative estimate of the distance between the camera and surface. Experiment 1 manipulated interpretations of these images by instructing two groups of participants to imagine a small or large distance between the camera and surface, while a third control group received no such instruction. In Experiments 2 and 3 interpretations were manipulated by providing visual cues for scale (e.g., objects of familiar size), which were presented alongside the target image or digitally inserted into the image. Results indicate that these manipulations can cause identical images to appear to belong to different material classes (e.g., water vs. marble), and that susceptibility to context information (i.e., material ambiguity) correlates with higher variability in distance estimates. Under challenging conditions, therefore, the recognition of some materials is vulnerable to simple manipulations of apparent scale.

Colour Variations within Light Fields: Interreflections and Colour Effects
Cehao Yu* (1), Elmar Eisemann (2), Sylvia Pont (1)
1: Perceptual Intelligence lab, TUDelft; 2: Computer Graphics and Visualization Group, TUDelft

The human visual system incorporates knowledge about local chromatic and lightness effects of interreflections (Bloj et al., Nature, 1999). Here we study basic principles behind chromatic effects of interreflections using computational modelling and photometric measurements. The colour of interreflections varies as a function of the number of bounces they went through. Using a computational model we found that those colour variations can show brightness, saturation and even hue shifts. Using a chromatic Mach Card, a concave folded card with both sides made of the same colour, we demonstrated those three types of colour effects empirically. Finally, we tested the effects of such coloured interreflections on light fields in 3D spaces. Via cubic spectral illuminance measurements in both computer simulations and full mock up room settings under different furnishing scenarios we measure the chromatic variations of first order properties of light fields. The types of chromatic variations were found to depend systematically on furnishing colour, lighting and geometry, as predicted, and also vary systematically within the light field, and thus throughout the space. We will next compare the physical light fields with visual light fields (including chromatic properties) and test perceived material colours, for (combinations of) the three types of effects.

Visual and haptic softness dimensions
Müge Cavdan* (1), Knut Drewing (1), Katja Doerschner (1,2,3)
1: Justus Liebig University Giessen, Germany; 2: Department of Psychology, Bilkent University, Ankara, Turkey; 3: National Magnetic Resonance Research Center, Bilkent University, Ankara, Turkey

When investigating visually or haptically perceived softness of materials researchers have typically equated softness with compliance. However, softness entails more aspects than this single dimension: a rabbit’s fur is soft in a different way than sand on Siesta beach and both’s softness is not necessarily related to the materials’ compliance. Here we investigated the dimensionality of perceived softness in visual and haptic domains. We asked participants to rate various materials on different adjectives. In the haptic experiment, participants were blindfolded and rated materials after haptically exploring them, whereas in the visual experiment they made the same ratings while looking at close up images of the same materials used in the haptic experiment. Principal component analyses revealed that both haptic and visual perception of softness are similarly organized in perceptual space, both containing dimensions of granularity, visco-elasticity, and deformability. However, furriness existed only in the haptic experiment. Moreover, the explained variance was higher in the haptic experiment, which suggests that the perceived dimensions of softness might be more accessible through haptic exploration than by looking at images of materials. Overall, these results contribute to our understanding of how visual and haptic information about material properties are processed and integrated.

Recognising materials over time
Ellen E M De Korte* (1), Andrew J Logan (2), Marina Bloj (1)
1: School of Optometry and Vision Science, University of Bradford, United Kingdom; 2:Department of Vision Sciences, Glasgow Caledonian University, United Kingdom

Materials change over time; colours fade and surfaces are scratched. These changes alter the retinal input and yet we still recognise them as the same material. When textiles are washed and laid out to dry we still identify them as the same fabric even though their colour visibly changes. The present study evaluated the appropriateness of an existing calibrated photograph set as a stimulus for studying the perception of appearance changes of materials over time. Participants (N = 4) reported which of the 2 pairs of images shown displayed the largest perceptual difference. Images were blocked (210 trials per block and participant) by material (Banana, Copper, Granite, Quilted Paper). Individual observers’ perceptual scales, estimated with Maximum Likelihood Difference Scaling via the General Linear Model estimation method, for each material were similar and showed that some, but not all, photographs were perceptually distinct. Thus, the calibrated photographs seem suitable for our purposes. Next steps will include image-based manipulations to establish which parameters drive the development of perceptual scales. Specifically, this will involve converting images to grayscale and manipulate image marks, such as brown staining in Banana images, in order to test the effects of colour and characteristic marks, respectively.