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Participants' eye movements were monitored while they read sentences in which high-frequency and low-frequency target words were presented either in normal font (e.g., account) or case alternated (e.g., aCcOuNt). The influence of the word frequency and case alternation manipulations on fixation times was examined. Although both manipulations had comparable effects on standard first-pass fixation measures, word frequency, but not case alternation was found to influence the duration of the first fixation in trials with multiple first-pass fixations. Assuming that lexical processing is more often incomplete at the termination of the first in multiple first-pass fixations than at the end of single first-pass fixations, the present findings provide strong evidence for an influence of word frequency on early lexical processing. Importantly, such a demonstration of a fast acting influence of a lexical variable on fixation times satisfies a critical prerequisite for establishing lexical control of eye movements in reading. Keywords: eye movements, reading, lexical processing, word frequency, case alternation DOI: 10.1037/a0019959

Humans can resolve the fine details of visual stimuli although the image projected on the retina is constantly drifting relative to the photoreceptor array. Here we demonstrate that the brain must take this drift into account when performing high acuity visual tasks. Further, we propose a decoding strategy for interpreting the spikes emitted by the retina, which takes into account the ambiguity caused by retinal noise and the unknown trajectory of the projected image on the retina. A main difficulty, addressed in our proposal, is the exponentially large number of possible stimuli, which renders the ideal Bayesian solution to the problem computationally intractable. In contrast, the strategy that we propose suggests a realistic implementation in the visual cortex. The implementation involves two populations of cells, one that tracks the position of the image and another that represents a stabilized estimate of the image itself. Spikes from the retina are dynamically routed to the two populations and are interpreted in a probabilistic manner. We consider the architecture of neural circuitry that could implement this strategy and its performance under measured statistics of human fixational eye motion. A salient prediction is that in high acuity tasks, fixed features within the visual scene are beneficial because they provide information about the drifting position of the image. Therefore, complete elimination of peripheral features in the visual scene should degrade performance on high acuity tasks involving very small stimuli. computation | fixational eye motion | neural network | retina | codex doi/ 10.1073/pnas.1006076107

The present study examined how proofreading and reading-for-comprehension instructions influence eye movements during reading. Thirty-seven participants silently read sentences containing compound words as target words while their eye movements were being recorded. We manipulated word length and frequency to examine how task instructions influence orthographic versus lexical--semantic processing during reading. Task instructions influenced both temporal and spatial aspects of eye movements: The initial landing position in words was shifted leftward, the saccade length was shorter, first fixation and gaze duration were longer, and refixation probability was higher during proofreading than during reading for comprehension. Moreover, in comparison to instructions for reading for comprehension, proofreading instructions increased both orthographic and lexical--semantic processing. This became apparent in a greater word length and word frequency effect in gaze duration during proofreading than during reading for comprehension. The present study suggests that the allocation of attentional resources during reading is significantly modulated by task demands. Keywords: eye movements, reading, task effects, proofreading DOI: 10.1037/a0020693

Recent research using word recognition paradigms, such as lexical decision and speeded pronunciation, has investigated how a range of variables affect the location and shape of response time distributions, using both parametric and non-parametric techniques. In this article, we explore the distributional effects of a word frequency manipulation on fixation durations in normal reading, making use of data from two recent eye movement experiments (Drieghe, Rayner, & Pollatsek, 2008; White, 2008). The ex-Gaussian distribution provided a good fit to the shape of individual subjects' distributions in both experiments. The frequency manipulation affected both the shift and skew of the distributions, in both experiments, and this conclusion was supported by the nonparametric vincentizing technique. Finally, a new experiment demonstrated that White's (2008) frequency manipulation also affects both shift and skew in response-time distributions in the lexical decision task. These results argue against models of eye movement control in reading that propose that word frequency influences only a subset of fixations and support models in which there is a tight connection between eye movement control and the progress of lexical processing. Keywords: eye movements in reading, word frequency, ex-Gaussian distribution DOI: 10.1037/a0016896

A word's frequency of occurrence and its predictability from a prior context are key factors determining how long the eyes remain on that word in normal reading. Past reaction-time and eye movement research can be distinguished by whether these variables, when combined, produce interactive or additive results, respectively. Our study addressed possible methodological limitations of prior experiments. Initial results showed additive effects of frequency and predictability. However, we additionally examined launch site (the distance from the pretarget fixation to the target) to index the extent of parafoveal target processing. Analyses revealed both additive and interactive effects on target fixations, with the nature of the interaction depending on the quality of the parafoveal preview. Target landing position and pretarget fixation time were also considered. Results were interpreted in terms of models of language processing and eye movement control. Our findings with respect to parafoveal preview and fixation time constraints aim to help parameterize eye movement behavior. Keywords: reading, eye movements, word frequency, contextual predictability, launch site DOI: 10.1037/a0020363

Three experiments explored whether patterns of eye movements during reading might help explain syntactic prominence effects that are typically observed using reaction time tasks. Participants read sentences in which target words were in syntactically prominent or syntactically less prominent positions. Across all three experiments, using three types of syntactic prominence manipulations, there were fewer fixations and shorter reading times for words in more prominent positions, indicating that enhanced accessibility of syntactically prominent words is not caused by increased processing time. Rather, syntactic prominence appears to facilitate early encoding/lexical access and sentence integration processes while also, as shown previously, increasing activation of concepts in a comprehender's sentence or discourse representation. We propose that enhanced encoding and sentence integration processes can be attributed to an increase in attentional resources for more prominent concepts, and that this increase derives from readers' immediate sensitivity to informational prominence contours that are signaled by syntax. doi: 10.3758/MC38.6.740

Eye movements in reading are sensitive to foveal and parafoveal word features. Whereas the influence of orthographic or phonological parafoveal information on gaze control is undisputed, there has been no reliable evidence for early parafoveal extraction of semantic information in alphabetic script. Using a novel combination of the gaze-contingent fast-priming and boundary paradigms, we demonstrate semantic preview benefit when a semantically related parafoveal word was available during the initial 125 ms of a fixation on the pretarget word (Experiments 1 and 2). When the target location was made more salient, significant parafoveal semantic priming occurred only at 80 ms (Experiment 3). Finally, with short primes only (20, 40, 60 ms), effects were not significant but were numerically in the expected direction for 40 and 60 ms (Experiment 4). In all experiments, fixation durations on the target word increased with prime durations under all conditions. The evidence for extraction of semantic information from the parafoveal word favors an explanation in terms of parallel word processing in reading. Keywords: eye movements, reading, parafoveal preview, semantic priming DOI: 10.1037/a0020233

Iron deficiency has been shown to impair dopamine functioning in rodent models, but it is challenging to obtain evidence of such effects in human infants. Because spontaneous eye-blink rate may provide a noninvasive assessment of dopamine functioning, we hypothesized that eye-blink rate would be lower in infants with iron-deficiency anemia and would increase with iron therapy. A 4-min eye-blink assessment was conducted for quiet, alert infants sitting on their mother's lap. Data were available for 61 9- to 10-mo-old infants from inner-city Detroit (19 iron-deficient anemic, 23 nonanemic iron-deficient, and 19 nonanemic iron-sufficient). Iron-deficient and iron-sufficient nonanemic groups had similar eye-blink rates (P = 0.90) and were therefore combined. We used Poisson regression based on generalized estimation equation methodology to test for differences between iron-deficient anemic and nonanemic infants in blinks/min and change after 3 mo of iron therapy. Iron-deficient anemic infants had a lower initial eye-blink rate than nonanemic infants (mean [+ or -] SD) (4.0 [+ or -] 1.9 vs. 5.3 [+ or -] 2.8 blinks/min; P = 0.02; effect size = 0.6 SD). At 12 me, eye-blink rate increased by 2.1 blinks/min in the iron- deficient anemic group (P = 0.008); there was no change in the nonanemic group (P = 0.96). These results are consistent with reduced dopamine function in iron-deficient anemic infants. The clinical importance of a lower eye-blink rate is unclear, but impaired dopamine functioning is likely to have broader impact, given the role dopamine plays in regulating movement, motivation, cognition, and hormone release. doi: 0.3945/jn.110.120964.

Routine human behavior has often been attributed to plans--mental representations of sequences goals and actions--but can also be attributed to more opportunistic interactions of mind and a structured environment. This study asks whether performance on a task traditionally analyzed in terms of plans can be better understood from a 'situated' (or 'embodied') perspective. A saccade-contingent display-updating paradigm is used to change the environment by adding, deleting, and moving task-relevant objects without participants' direct awareness. Response latencies, action patterns, and eye movements all indicate that performance is guided not by plans stored in memory but by a control routine bound to objects as needed by perception and selective attention. The results have implications for interpreting everyday task performance and particular neuropsychological deficits. Keywords: selective attention, eye movements, Tower of Hanoi, situated cognition, problem solving DOI: 10.1037/a0018268

We continuously move our eyes when we inspect a visual scene. Although this leads to a rapid succession of discontinuous and fragmented retinal snapshots, we perceive the world as stable and coherent. Neural mechanisms underlying visual stability may depend on internal monitoring of planned or ongoing eye movements. In the macaque brain, a pathway for the transmission of such signals has been identified that is relayed by central thalamic nuclei. Here, we studied a possible role of this pathway for perceptual stability in a patient with a selective lesion affecting homologous regions of the human thalamus. Compared with controls, the patient exhibited a unilateral deficit in monitoring his eye movements. This deficit was manifest by a systematic inaccuracy both in successive eye movements and in judging the locations of visual stimuli. In addition, perceptual consequences of oculomotor targeting errors were erroneously attributed to external stimulus changes. These findings show that the human brain draws on transthalamic monitoring signals to bridge the perceptual discontinuities generated by our eye movements. saccade | corollary discharge | efference copy | extraretinal doi/10.1073/pnas.0910742107

Initiating an eye movement is slowed if the saccade is directed to a location that has been fixated in the recent past. We show that this inhibitory effect is modulated by the temporal statistics of the environment: if a return location is likely to become behaviorally relevant, inhibition of return is absent. By fitting an accumulator model of saccadic decision-making, we show that the inhibitory effect and the sensitivity to local statistics can be dissociated in their effects on the rate of accumulation of evidence, and the threshold controlling the amount of evidence needed to generate a saccade. decision-making | computational modeling | saccadic eye movements | reaction time | accumulator models www.pnas.org/cgi/doi/10.1073/pnas.0906845107

When trained on a serial-order task to respond to 5 simultaneously displayed stimuli, monkeys (Macaca fascicularis) show an elevated latency to respond to the first item (A) or the first 2 items (A and B) followed by short and uniform latencies to respond to the remaining items. This pattern has been interpreted as evidence of planning, with the long initial latency reflecting the animal planning their responses, and the subsequent short and uniform latencies reflecting the execution of the planned responses. An analysis of eye movements, however, revealed no evidence of planning. The elevated latency to item A is likely an artifact of the method of stimulus display. Keywords: planning, serial order, eye movements, monkeys DOI: 10.1037/a0014020

An early interest in cognitive processes led me to study with Mike Posner from whom I acquired the intellectual tools to follow Hebb's (1949) advice that 'Everyone knows that attention and set exist so we had better get the skeleton out of the closet and see what can be done with it.' Using variants of the model task Posner developed for exploring the control of visual attention we have demonstrated that endogenous shifts of attention are not generated by unexecuted oculomotor activation, that endogenous and exogenous shifts of attention are fundamentally different on a variety of dimensions and that an aftermath of exogenous (but not endogenous) orienting, inhibition of return, facilitates search by encouraging orienting to novel items. A research strategy for understanding ambiguous forms of orienting (e.g., that controlled by conspecific gaze) is proposed. Keywords: attention, endogenous, exogenous, inhibition of return, eye movements

During the preparation of saccadic eye movements, visual attention is confined to the target of intended fixation and there is a corresponding diminution of visual sensitivity at nontarget locations. Neurons within the macaque visual cortex exhibit correlates of these perceptual changes, such as in area V4, where neuronal responses are enhanced during the preparation of saccades to stimuli within the receptive field (RF), and responses are suppressed during the preparation of saccades to other locations. Both the perceptual and neurophysiological effects suggest that the sensitivity of visual cortical neurons to input is dynamic during saccade preparation. We probed the contrast sensitivity of area V4 neurons to nontarget stimuli at varying times during the preparation of saccades to locations outside of the neuron's receptive field. We found that the contrast sensitivity of many neurons is profoundly altered within 50 ms of saccade onset. The luminance or color contrast sensitivity of individual V4 neurons could increase, decrease, or remain unchanged before saccade onset. For luminance contrast sensitivity, decreases in sensitivity were more frequent and larger in magnitude, resulting in an overall decrement in sensitivity across the population. For color contrast, the effects were smaller and more heterogeneous, resulting in little or no overall change in sensitivity across the population. Our results demonstrate the dynamic influence that saccade preparation has on the sensitivity of visual cortical neurons and suggest a basis for the changes in perception known to occur during saccade preparation. oculomotor | saccadic suppression | transaccadic integration | visuomotor integration | perceptual constancy