Binocular foveation in reading

On the distinction between position and order information when processing strings of characters

To probe the processing of gaze-dependent positional information and gaze-independent order information when matching strings of characters, we compared effects of visual similarity (hypothesized to affect gaze-centered position coding) with the effects of character transpositions (hypothesized to affect the processing of gaze-independent order information). In Experiment 1, we obtained empirical measures of visual similarity for pairs of characters, separately for uppercase consonants and keyboard symbols. These similarity values were then used in Experiment 2 to create pairs of four-character stimuli (four letters or four symbols) that could differ by substituting one character with a different character from the same category that was visually similar (e.g., FJDK-FJBK) or dissimilar (e.g., FJVK-FJBK). We also compared the effects of transposing two characters (e.g., FBJK-FJBK) with substituting two characters (e.g., FHSK-FJBK). "Different" responses were harder to make in the single substitution condition when the substituted character was visually similar, and this effect was not conditioned by character type. On the other hand, transposition costs (i.e., greater difficulty in detecting a difference with transpositions compared with double substitutions) were greater for letters compared with symbols. We conclude that visual similarity mainly affects the generic gaze-dependent processing of complex visual features, and that the encoding of letter order involves a mechanism that is specific to reading.

Small temporal asynchronies between the two eyes in binocular reading: Crosslinguistic data and the implications for ocular prevalence

We investigated small temporal nonalignments between the two eyes’ fixations in the reading of English and Chinese. We define nine different patterns of asynchrony and report their spatial distribution across the screen of text. We interpret them in terms of their implications for ocular prevalence—prioritizing the input from one eye over the input from the other eye in higher perception/cognition, even when binocular fusion has occurred. The data are strikingly similar across the two very different orthographies. Asynchronies, in which one eye begins the fixation earlier and/or ends it later, occur most frequently in the hemifield corresponding to that eye. We propose that such small asynchronies cue higher processing to prioritize the input from that eye, during and after binocular fusion.

An investigation of parafoveal masks with the incremental boundary paradigm

Most of what we know about parafoveal preprocessing during reading is based on the boundary paradigm in combination with parafoveal masks as a presumably neutral baseline condition. Recent evidence questions the neutrality of the baseline condition by showing that parafoveal masks inflict preview costs. Using a novel, incremental boundary paradigm we studied the effect of parafoveal masks. Manipulating the salience of parafoveal previews, we found that increasing salience of the masks resulted in increasingly longer fixation times on target words, but also on pretarget words-suggesting preview costs. We conclude that the hidden preview costs of parafoveal masks in the classical boundary paradigm inflate the processing times for the baseline condition and hence lead to an overestimation of the preview benefit. Thus, the present study questions the validity of some of the conclusions drawn on the basis of the classical boundary paradigm.

Investigating eye movement acquisition and analysis technologies as a causal factor in differential prevalence of crossed and uncrossed fixation disparity during reading and dot scanning

Previous studies examining binocular coordination during reading have reported conflicting results in terms of the nature of disparity (e.g. Kliegl, Nuthmann, & Engbert (Journal of Experimental Psychology General 135:12-35, 2006); Liversedge, White, Findlay, & Rayner (Vision Research 46:2363-2374, 2006). One potential cause of this inconsistency is differences in acquisition devices and associated analysis technologies. We tested this by directly comparing binocular eye movement recordings made using SR Research EyeLink 1000 and the Fourward Technologies Inc. DPI binocular eye-tracking systems. Participants read sentences or scanned horizontal rows of dot strings; for each participant, half the data were recorded with the EyeLink, and the other half with the DPIs. The viewing conditions in both testing laboratories were set to be very similar. Monocular calibrations were used. The majority of fixations recorded using either system were aligned, although data from the EyeLink system showed greater disparity magnitudes. Critically, for unaligned fixations, the data from both systems showed a majority of uncrossed fixations. These results suggest that variability in previous reports of binocular fixation alignment is attributable to the specific viewing conditions associated with a particular experiment (variables such as luminance and viewing distance), rather than acquisition and analysis software and hardware.

Foveational complexity in single word identification: contralateral visual pathways are advantaged over ipsilateral pathways

Recognition of a single word is an elemental task in innumerable cognitive psychology experiments, but involves unexpected complexity. We test a controversial claim that the human fovea is vertically divided, with each half projecting to either the contralateral or ipsilateral hemisphere, thereby influencing foveal word recognition. We report a novel haploscope task: the two halves of a four-letter word were briefly presented to the two eyes in a Both condition (st|ep)(st|ep), a Contralateral condition (st|__)(__|ep), or an Ipsilateral condition (__|ep)(st|__), all yielding the same single word percept (step). The Both condition yielded superior perceptual recognition, followed by the contralateral projection, then the ipsilateral projection. These results demonstrate that the structure of the fovea influences even the recognition of short, foveally presented words. Projecting different parts of the same word to different hemispheres involves unforeseen complexities and opportunities for optimizing hemispheric coordination.