The IOVP effect in mindless reading: Experiment and modeling

AbstractFixation durations in reading are longer for within-word fixation positions close to word center than for positions near word boundaries. This counterintuitive result was termed the Inverted-Optimal Viewing Position (IOVP) effect. We proposed an explanation of the effect based on error-correction of mislocated fixations [Nuthmann, A., Engbert, R., & Kliegl, R. (2005). Mislocated fixations during reading and the inverted optimal viewing position effect. Vision Research, 45, 2201–2217], that suggests that the IOVP effect is not related to word processing. Here we demonstrate the existence of an IOVP effect in “mindless reading”, a z-string scanning task. We compare the results from experimental data with results obtained from computer simulations of a simple model of the IOVP effect and discuss alternative accounts. We conclude that oculomotor errors, which often induce mislocalized fixations, represent the most important source of the IOVP effect

Oculomotor control in a sequential search task

AbstractUsing a serial search paradigm, we observed several effects of within-object fixation position on spatial and temporal control of eye movements: the preferred viewing location, launch site effect, the optimal viewing position, and the inverted optimal viewing position of fixation duration. While these effects were first identified by eye-movement studies in reading, our approach permits an analysis of the functional relationships between the effects in a different paradigm. Our results demonstrate that the fixation position is an important predictor of the subsequent saccade by influencing both fixation duration and the selection of the next saccade target

Mislocated fixations during reading and the inverted optimal viewing position effect

AbstractRefixation probability during reading is lowest near the word center, suggestive of an optimal viewing position (OVP). Counterintuitively, fixation durations are largest at the OVP, a result called the inverted optimal viewing position (IOVP) effect [Vitu, McConkie, Kerr, & O’Regan, (2001). Vision Research 41, 3513–3533]. Current models of eye-movement control in reading fail to reproduce the IOVP effect. We propose a simple mechanism for generating this effect based on error-correction of mislocated fixations due to saccadic errors. First, we propose an algorithm for estimating proportions of mislocated fixations from experimental data yielding a higher probability for mislocated fixations near word boundaries. Second, we assume that mislocated fixations trigger an immediate start of a new saccade program causing a decrease of associated durations. Thus, the IOVP effect could emerge as a result of a coupling between cognitive and oculomotor processes

Modelling fixation locations using spatial point processes

Whenever eye movements are measured, a central part of the analysis has to do with where subjects fixate, and why they fixated where they fixated. To a first approximation, a set of fixations can be viewed as a set of points in space: this implies that fixations are spatial data and that the analysis of fixation locations can be beneficially thought of as a spatial statistics problem. We argue that thinking of fixation locations as arising from point processes is a very fruitful framework for eye movement data, helping turn qualitative questions into quantitative ones. We provide a tutorial introduction to some of the main ideas of the field of spatial statistics, focusing especially on spatial Poisson processes. We show how point processes help relate image properties to fixation locations. In particular we show how point processes naturally express the idea that image features' predictability for fixations may vary from one image to another. We review other methods of analysis used in the literature, show how they relate to point process theory, and argue that thinking in terms of point processes substantially extends the range of analyses that can be performed and clarify their interpretation.Comment: Revised following peer revie

Self-recognition generates characteristic responses in pupil dynamics and microsaccade rate

Visual fixation is an active process with pupil dynamics as well as fixational eye movements and microsaccades that support perception. Measures of both pupil contraction and microsaccades are known to be sensitive to ongoing cognition and emotional processing. Here we present experimental results from a visual fixation task demonstrating that pupil size and microsaccade rate respond differently during self-recognition (when seeing one's own face) than when seeing familiar or unfamiliar faces. First, the pupil response is characterized by an immediate pupil-constriction followed by later dilation in response to stimulus onsets. For one's own face, we observe muted constriction and greater dilation compared to other faces. Second, microsaccades, which generally show an inhibitory response to incoming stimuli, are more strongly inhibited in response to one's own face compared to other faces. Our results lend support to the idea that eye-related physiological measures could contribute to biometric identification procedures