Research projects

Lincoln 2015-

In 2015 I joined the School of Psychology at the University of Lincoln. I started a blog to document ongoing research.

Aberdeen 2012-2015

During my lectureship at the university of Aberdeen, I supervised several student projects (thesis projects and volunteering work) and was engaged in my own experiments. Descriptions of the thesis projects can be found here and here. Most of the projects involved eye movement recordings, but there were also studies using response times measures.

Leuven 2010-2012

In my research project, funded by FWO, I have investigated perceptual grouping using response times and eye movement measures. This work was conducted in collaboration with several people. Research investigating how perceptual grouping affects eye movement metrics was conducted together with Tandra Ghose and Johan Wagemans. A project examining eye movements during art perception, involved a collaboration with Ruth Loos and Johan Wagemans (see Ruth Loos' project website and the i-Perception paper: Loos, 2012). Other work involved eye movements in contour integration (with Nathalie van Humbeeck, Udo Ernst and Johan Wagemans), the use of survival analysis to study visual masking (with Sven Panis and Johan Wagemans),  a regions of interest analysis for dynamic stimuli (with Kris Evers, Peter de GraefRudy Dekeerschieter, and Johan Wagemans), response inhibition in the saccadic Stroop task, and the influence of advertisements on eye movements during economic decision making.

RHUL 2009


This ESRC funded research project, carried out in the lab of Robin Walker, investigated whether social cues, such as someone's gaze, automatically shift the observer's attention and induce an automatic response, such as an eye movement in the gazed-at or pointed-at direction. To investigate such automatic response preparation also when no overt response is made, the small movements of  the eyes (known as 'microsaccades') are analyzed. In addition, on a portion of the trials, participants are asked to make a saccade to a target object elsewhere in the display, so that the trajectories of these saccadic eye movements can be analyzed for signs of the suppression of an automatic response to the social cue, for example, by looking at the curvature of the saccade trajectory. 

Marseille 2008


In this project, carried out in the lab of Françoise Vitu (continued by Christophe Tandonnet), the role of the 'global effect'  in reading is studied. When we make an eye movements towards a target in the presence of distractor, the eyes often land in between the target and the distractor (the 'global effect'; Findlay 1982). This effect seems to reflect competition between the possible saccade targets during the preparation of an eye movement.

Example of an eye movement towards the target (large circle) in the presence of a distractor (small circle). The eye lands in between the two circles after which a second eye movement is made to bring the eyes to the location of the target (the 'global effect').






RHUL 2007-2008


My project at Royal Holloway University of London, carried out in the labs of Johannes Zanker and Robin Walker at Royal Holloway University of London, focused on the eye movements that people make while they try not to move their eyes, known as fixational eye movements (eye movements during visual fixation). These fixational eye movements can be classified into three categories: Tremor, which are small, but fast movements of the eye, drift, which are large but slow movements, and microsaccad es, which are fast and relatively large eye movements (compared to tremor).

One part of the project involved the study of fixational eye movements while looking at Op Art. Some of these Op Art paintings, such as Bridget Riley's "Fall" (1963), induce strong motion percepts
.It was hypothesized that the motion illusion originates from the small eye movements that people make while fixating an object (see Zanker & Walker, 2004). Previous research focused on the role of micro-saccades in the illusory motion. In my project, we investigated what role drift plays.




Example of an eye movement trace during visual fixation with microsaccades (blue) and without (red). Examples like these seem to suggest that microsaccades bring the eyes back to the fixation point.
 

In the second part of my research project, we investigated of the origin of microsaccades and their role in visual attention. For this, we determined the effect of different cues as to where to move the eyes (peripheral target, arrow cue) on the rate and the direction of microsaccades before the onset of the eye movement.



Microsaccade rate as a function of the time after the onset of a peripherally presented arrow cue. Participants were asked to make a saccade to the place-holder which was pointed at by the arrow. In response to the onset of the arrow, micro-saccades first become less frequent (inhibition phase), followed by an increase in the number of micro-saccades. This is a typical pattern found for different types of cues (visual, auditory).






EPFL 2004-2007

The focus of my work in the lab of Michael Herzog at the Ecole Polytechnique Federale de Lausanne (EPFL) was on visual masking. In visual masking, a target stimulus is rendered less visible by a masking stimulus, which is presented before ('forward masking'), after ('backward masking') the target
, or at the same time as the target ('simultaneous masking'). Whereas past research has demonstrated the importance of temporal aspects, such as the relative timing of the stimuli and their durations, we found that spatia l aspects, such as the spatial layout of the target and the mask, are equally important. For example, by increasing the length of two lines in a mask consisting of 25 lines, its effect on a preceding target strongly increased (see Hermens & Herzog, 2007). Many of these effects could well be modeled with a simple model applying lateral inhibition and excitation only (see Hermens & Ernst, 2007), suggesting that although many effects seemed to involve complex grouping operations, they can actually be implemented in terms of low-level visual interactions.



The effect of the mask layout on the masking strength (strong masking -> high thresholds). From: Hermens & Herzog, 2007.







A second line of research involved feature fusion. If two stimuli are presented in rapid succession, their features can fuse. For example, a green disc followed by a red disc can appear yellow. Together with Frank Scharnowski, we have investigated the underlying mechanisms of the fusion of stimulus features providing evidence for two types of visual memory (one in which information decays quickly, and one which holds information longer).

Utrecht 2004

Part of my PhD project involved the study of haptic orientation perception. In three experiments, carried out in the lab of Astrid Kappers, participants were asked to either (1) match the orientation of two bars, (2) report the orientation of a bar, or (3) set bars in particular orientation. In the matching task (task 1) participants made large systematic errors. However, no such errors were found for orientation perception and production (tasks 2 and 3).



Participants, who were blindfolded, were asked to match the orientation of two bars.




RU Nijmegen 2001-2004

My PhD project, conducted in the lab of Stan Gielen, focussed on the perception of object orientation. If participants are asked to match the orientation of a bar, they make systematic errors. These errors also affect the interception of an approaching line.



Illustration of the experimental setup demonstrating a distortion of the perceived orientation of objects.







PSU 2003

During a four months research project in the lab of David Rosenbaum at Penn State University, funded by a Fulbright grant, we investigated the planning of grasping movements. Participants were asked to grasp a salad bowl and to bring it to one of several predefined positions and put it into a particular orientation. In contrast to previous findings, we did not find that participants chose their grasp according to target position and orientation of the bowl.


Illustration of the experimental setup in which the participants' arm movements were recorded while they grasped a bowl.








MPI 1999-2000

In my MA project, carried out at the Max Plank Institute for psycholinguistics in Nijmegen, the retrieval of words from the mental lexicon in language production was investigated. Participants were asked to name two or more pictures presented on the screen in one phrase such as `The bike and the arrow'. By measuring response times and recording eye movements, we investigated whether retrieving the names of the two pictures interfered, and whether such interference depended on whether the names were semantically related ('The apple and the pear') or phonologically related ('The book and the cook').


Pattern of fixations while naming the two pictures in a phrase like 'The bike and the arrow'.

Subpages (1): Recent student projects