Direct control of fixation times in scene viewing: Evidence from analysis of the distribution of first fixation duration

Participants' eye movements were monitored in two scene viewing experiments that manipulated the task-relevance of scene stimuli and their availability for extrafoveal processing. In both experiments, participants viewed arrays containing eight scenes drawn from two categories. The arrays of scenes were either viewed freely (Free Viewing) or in a gaze-contingent viewing mode where extrafoveal preview of the scenes was restricted (No Preview). In Experiment 1a, participants memorized the scenes from one category that was designated as relevant, and in Experiment 1b, participants chose their preferred scene from within the relevant category. We examined first fixations on scenes from the relevant category compared to the irrelevant category (Experiments 1a and 1b), and those on the chosen scene compared to other scenes not chosen within the relevant category (Experiment 1b). A survival analysis was used to estimate the first discernible influence of the task-relevance on the distribution of first-fixation durations. In the free viewing condition in Experiment 1a, the influence of task relevance occurred as early as 81 ms from the start of fixation. In contrast, the corresponding value in the no preview condition was 254 ms, demonstrating the crucial role of extrafoveal processing in enabling direct control of fixation durations in scene viewing. First fixation durations were also influenced by whether or not the scene was eventually chosen (Experiment 1b), but this effect occurred later and affected fewer fixations than the effect of scene category, indicating that the time course of scene processing is an important variable mediating direct control of fixation durations.     

Eye movement control during scene viewing: Immediate degradation and enhancement effects of spatial frequency filtering

What controls how long the eyes remain fixated during scene perception? We investigated whether fixation durations are under the immediate control of the quality of the current scene image. Subjects freely viewed photographs of scenes in preparation for a later memory test while their eye movements were recorded. Using the saccade-contingent display change method, scenes were degraded (Experiment 1) or enhanced (Experiment 2) via blurring (low-pass filtering) during predefined saccades. Results showed that fixation durations immediately after a display change were influenced by the degree of blur, with a monotonic relationship between degree of blur and fixation duration. The results also demonstrated that fixation durations can be both increased and decreased by changes in the degree of blur. The results suggest that fixation durations in scene viewing are influenced by the ease of processing of the image currently in view. The results are consistent with models of saccade generation in scenes in which moment-to-moment difficulty in visual and cognitive processing modulates fixation durations.     

Spatial frequency filtering and the direct control of fixation durations during scene viewing

The present study employed a saccade-contingent change paradigm to investigate the effect of spatial frequency filtering on fixation durations during scene viewing. Subjects viewed grayscale scenes while encoding them for a later memory test. During randomly chosen saccades, the scene was replaced with an alternate version that remained throughout the critical fixation that followed. In Experiment 1, during the critical fixation, the scene could be changed to high-pass and low-pass spatial frequency filtered versions. Under both conditions, fixation durations increased, and the low-pass condition produced a greater effect than the high-pass condition. In subsequent experiments, we manipulated the familiarity of scene information during the critical fixation by flipping the filtered scenes upside down or horizontally. Under these conditions, we observed lengthening of fixation durations but no difference between the high-pass and low-pass conditions, suggesting that the filtering effect is related to the mismatch between information extracted within the critical fixation and the ongoing scene representation in memory. We also conducted control experiments that tested the effect of changes to scene orientation (Experiment 2a) and the addition of color to a grayscale scene (Experiment 2b). Fixation distribution analysis suggested two effects on the distribution fixation durations: a fast-acting effect that was sensitive to all transsaccadic changes tested and a later effect in the tail of the distribution that was likely tied to the processing of scene information. These findings are discussed in the context of theories of oculomotor control during scene viewing.     

A perceptual-economy account for the inverted-optimal viewing position effect

In reading, fixation durations are longer when the eyes fall near the center of words than when fixation occurs toward the words' ends-the inverted-optimal viewing position (I-OVP) effect. This study assessed whether the I-OVP effect was based on the fixation position in the word or the fixation position in the visual stimulus. In Experiments 1-3, words were presented at variable locations within longer strings of symbols. On trials with short fixation durations, there were effects of fixation position in the string. When long fixations were made, there were effects of fixation position in the word. In Experiment 4, an I-OVP effect was found for meaningless number strings, and its strength depended on the task's processing demands. The findings show that (a) the I-OVP effect is unrelated to orthographic informativeness and (b) the eyes are not constrained to spend more time at the center of visual stimuli. These results support a perceptual-economy account: Fixations are held longer when the eyes are estimated to be at locations in words/stimuli in which greater amounts of information are anticipated. Implications for eye movements in reading are discussed.     

Orthographic familiarity influences initial eye fixation positions in reading

An important issue in the understanding of eye movements in reading is what kind of nonfoveal information can influence where we move our eyes. In Experiment 1, first fixation landing positions were nearer the beginning of misspelled words. Experiment 2 showed that the informativeness of word beginnings does not influence where words are first fixated. In both experiments, refixations were more likely to be to the left of the initial fixation position if the words were misspelled. Also, there was no influence of spelling on prior fixation durations or refixation probabilities, that is, there was no evidence for parafoveal‐on‐foveal effects. The results show that the orthographic familiarity, but not informativeness, of word initial letter sequences influences where words are first fixated.     

Reading with a filtered fovea: The influence of visual quality at the point of fixation during reading

Reading relies critically on processing text in foveal vision during brief fixational pauses, and high-quality visual input from foveal text is fundamental to theories of reading. However, the quality of visual input from foveal text that is actually functional for reading and the effects of this input on reading performance are unclear. To investigate these issues, a moving, gaze-contingent foveal filtering technique was developed to display areas of text within foveal vision that provided only coarse, medium, or fine scale visual input during each fixational pause during reading. Normal reading times were unaffected when foveal text up to three characters wide at the point of fixation provided any one visual input (coarse, medium, or fine). Wider areas of coarse visual input lengthened reading times, but reading still occurred, and normal reading times were completely unaffected when only medium or fine visual input extended across the entire fovea. Further analyses revealed that each visual input had no effect on the number of fixations made when normal text was read, that adjusting fixation durations helped preserve reading efficiency for different visual inputs, and that each visual input had virtually no effect on normal saccades. These findings indicate that, despite the resolving power of foveal vision and the emphasis placed on high-quality foveal visual input by theories of reading, normal reading functions with similar success using a range of restricted visual inputs from foveal text, even at the point of fixation. Some implications of these findings for theories of reading are discussed.     

When attractiveness demands longer looks: The effects of situation and gender

We investigated how aesthetics guides our exploration of the environment. We embedded attractive and nonattractive faces into complex, real-world scenes and measured eye movements during scene viewing. We examined whether attractive faces would elicit longer looks, which would suggest that the aesthetic response orients people toward the rewarding and pleasing aspects of the environment. Experiment 1 showed that mean fixation, mean first fixation, and total fixation durations were longer to attractive faces, and fixations were longest to female faces and by female perceivers. In Experiment 2, we examined whether these effects of attractiveness are sensitive to situational factors. When perceivers were subjected to a threat or social approach manipulation prior to viewing the scenes, we confirmed specific hypotheses concerning the two manipulations. In accordance with the hypothesis that males have higher aggression potential than females, there were no differences in fixation durations between attractive and nonattractive male faces in the threat condition. On the other hand, in the social approach condition, both female and male attractive faces received longer looks. These results suggest that the aesthetic response orients people not only to the pleasing aspects of their environment, but also to those features that are adaptively relevant.     

Effects of foveal processing difficulty on the perceptual span in reading: implications for attention and eye movement control

Two experiments were conducted to examine the effects of foveal processing difficulty on the perceptual span in reading. Subjects read sentences while their eye movements were recorded. By changing the text contingent on the reader's current point of fixation, foveal processing difficulty and the availability of parafoveal word information were independently manipulated. In Experiment 1, foveal processing difficulty was manipulated by lexical frequency, and in Experiment 2 foveal difficulty was manipulated by syntactic complexity. In both experiments, less parafoveal information was acquired when processing in the fovea was difficult. We conclude that the perceptual span is variable and attentionally constrained. We also discuss the implications of the results for current models of the relation between covert visual-spatial attention and eye movement control in reading.     

Fixation durations in scene viewing: Modeling the effects of local image features,oculomotor parameters,and task

Scene perception requires the orchestration of image- and task-related processes with oculomotor constraints. The present study was designed to investigate how these factors influence how long the eyes remain fixated on a given location. Linear mixed models (LMMs) were used to test whether local image statistics (including luminance, luminance contrast, edge density, visual clutter, and the number of homogeneous segments), calculated for 1° circular regions around fixation locations, modulate fixation durations, and how these effects depend on task-related control. Fixation durations and locations were recorded from 72 participants, each viewing 135 scenes under three different viewing instructions (memorization, preference judgment, and search). Along with the image-related predictors, the LMMs simultaneously considered a number of oculomotor and spatiotemporal covariates, including the amplitudes of the previous and next saccades, and viewing time. As a key finding, the local image features around the current fixation predicted this fixation’s duration. For instance, greater luminance was associated with shorter fixation durations. Such immediacy effects were found for all three viewing tasks. Moreover, in the memorization and preference tasks, some evidence for successor effects emerged, such that some image characteristics of the upcoming location influenced how long the eyes stayed at the current location. In contrast, in the search task, scene processing was not distributed across fixation durations within the visual span. The LMM-based framework of analysis, applied to the control of fixation durations in scenes, suggests important constraints for models of scene perception and search, and for visual attention in general.     

Eye movements and word skipping during reading revisited

The authors examined word skipping in reading in 2 experiments. In Experiment 1, skipping rates were higher for a preview of a predictable word than for a visually similar nonword, indicating there is full recognition in parafoveal vision. In Experiment 2, foveal load was manipulated by varying the frequency of the word preceding either a 3-letter target word or a misspelled preview. There was again a higher skipping rate for a correct preview and a lower skipping rate when there was a high foveal load, but there was no interaction, and the pattern of effects in fixation times was the same as in the skipping data. Experiment 2 also showed significant skipping of nonwords similar to the target word, indicating skipping based on partial information.     

Encoding of text, manual movement planning, and eye-hand coordination during copytyping.

Typing span and coordination of word viewing times with word typing times in copytyping were examined. In Experiment 1, typists copied passages of text while their eye movements were measured. Viewing location was determined during each eye fixation and was used to control the amount of usable visual information. Viewing constraints decreased interword saccade size when fewer than 7 character spaces of text were visible to the right of fixation and increased interkeypress times when fewer than 3 character spaces of text were visible. The eye-hand span amounted to 2.8 character spaces. Experiment 2 revealed increases in word typing times and word viewing times as biomechanic typing difficulty increased and word frequency decreased. These findings are consistent with a model of eye-hand coordination that postulates that eye-hand coordination involves central and peripheral processes.     

Attention demands during reading and the occurrence of brief (express) fixations

Eye movements were recorded while subjects read passages of text repeatedly (Experiment 1) and while normal text and strings ofhomogeneous letters were fixated (Experiment 2). Text repetition decreased fixation durations and increased saccade size, presumably because it decreased attention demands. Irrespective ofrepetition, however, no distinct distribution of brief (express) fixations emerged. In Experiment 2, fixation durations were shorter and saccades were larger when strings of homogeneous letters were “read,” indicating that this condition decreased attention demands. Again, however, no distinct distribution of express fixations emerged. These findings pose problems for the view that attentional processes determine the occurrence of brief (express) fixation durations in reading. Supplementary analyses of Experiments 1 and 2 suggested that visuospatial processing affected fixation durations, irrespective of linguistic processing demands.     

Brief foveal masking during scene perception

In the present experiment, participants were exploring line drawings of scenes in the context of an object-decision task, while eye-contingent display changes manipulated the appearance of the foveal part of the image. Foveal information was replaced by an ovoid noise mask for 83 ms, after a preset delay of 15, 35, 60, or 85 ms following the onset of fixations. In control conditions, a red ellipse appeared for 83 ms, centered around the fixation position, after the same delays as in the noise-mask conditions. It was found that scene exploration was hampered especially when foveal masking occurred early during fixations, replicating earlier findings. Furthermore, fixation durations were shown to increase linearly as the mask delay decreased, which validates the fixation duration as a measure of perceptual processing speed.     

Lexical access during eye fixations in reading: effects of word-initial letter sequence

Two experiments tested the hypothesis that lexical access in reading is initiated on the basis of word-initial letter information obtainable in the parafoveal region. Eye movements were monitored while college students read sentences containing target words whose initial trigram (Experiment 1) or bigram (Experiment 2) imposed either a high or a low degree of constraint in the lexicon. In contradiction to our hypothesis, high-constraint words (e.g., DWARF) received longer fixations than did low-constraint words (e.g., CLOWN), despite the fact that high-constraint words have an initial letter sequence shared by few other words in the lexicon. Moreover, a comparison of fixation times in viewing conditions with and without parafoveal letter information showed that the amount of decrease in target fixation time due to prior parafoveal availability was the same for high-constraint and low-constraint targets. We concluded that increased familiarity of word-initial letter sequence is beneficial to lexical access and that familiarity affects the efficiency of foveal but not parafoveal processing.     

The effects of collaboration on recall of social information

Three experiments examined the effects of passage type on both individual and collaborative memory performance. In Experiment 1, both individuals and collaborative groups recalled more information from passages containing social information than non-social information. Furthermore, collaborative inhibition (CI) was observed for both types of passages. In Experiment 2, which included a social passage that did not contain gossip, significant main effects of both gossip (gossip > non-gossip) and sociability (explicit > implicit) were observed. As in Experiment 1, CI was observed across all conditions. Experiment 3 separately manipulated gossip and the interest level of the passages and both of these factors enhanced memory performance. Moreover, robust CI was again observed across all conditions. Taken together, the present results demonstrate a mnemonic benefit for social information in individuals and collaborative groups.     

Effects of foveal priming and extrafoveal preview on object identification

The results of three different experiments suggested that the relation between an object in the fovea on fixation n and an object subsequently brought into the fovea on fixation n + 1 affects the time to identify the second object. In Experiment 1 we extended previous work by demonstrating that a previously seen related priming object speeded the time to name a target object even when a saccade intervened between the two objects. In Experiment 2 we replicated this result and further showed that the benefit on naming time was due to facilitation from the related object rather than inhibition from the unrelated object. In addition, naming of the target object was much slower in both experiments when there was not a peripheral preview of the target object on fixation n. However, because the effect of the foveal priming object was greater when the target was not present than when it was present, priming did not appear to make extraction of the extrafoveal information more efficient. In Experiment 3, fixation times were recorded while subjects looked at four objects in order to identify them. Fixation time on an object was shorter when a related object was fixated immediately before it, even though the four objects did not form a scene. The size of the facilitation was roughly comparable to that in several analogous experiments where scenes were used. The results suggest that the effects of a predictive scene context on object identification may be explainable in terms of an object-to-object or "intralevel" priming mechanism.     

Affective significance enhances covert attention: Roles of anxiety and word familiarity

To investigate the processing of emotional words by covert attention, threat-related, positive, and neutral word primes were presented parafoveally (2.2° away from fixation) for 150 ms, under gaze-contingent foveal masking, to prevent eye fixations. The primes were followed by a probe word in a lexical-decision task. In Experiment 1, results showed a parafoveal threat–anxiety superiority: Parafoveal prime threat words facilitated responses to probe threat words for high-anxiety individuals, in comparison with neutral and positive words, and relative to low-anxiety individuals. This reveals an advantage in threat processing by covert attention, without differences in overt attention. However, anxiety was also associated with greater familiarity with threat words, and the parafoveal priming effects were significantly reduced when familiarity was covaried out. To further examine the role of word knowledge, in Experiment 2, vocabulary and word familiarity were equated for low- and high-anxiety groups. In these conditions, the parafoveal threat–anxiety advantage disappeared. This suggests that the enhanced covert-attention effect depends on familiarity with words.     

Size scaling and its effect on letter detection

Two ways of scaling letter size across eccentricity were investigated in a choice reaction time (CRT) task. Experiments 1 and 2 tested cortical magnification theory (M-scaling), while Experiment 3 used scaled sizes drawn from Anstis’s regression formula (A-scaling). Experiment 4 compared both scaling techniques, together with the effect of exposure duration and the absolute size of the foveal letter. Results showed that scaling effectiveness improved when large rather than small foveal letters were used. A-scaling with a large foveal letter provided a good fit for the data at parafoveal locations, but underestimated the letter sizes needed at large eccentricities. M-scaling with a large foveal letter size produced CRTs that were independent of eccentricity. Exposure duration did not substantially affect performance.     

Affective significance enhances covert attention: roles of anxiety and word familiarity

To investigate the processing of emotional words by covert attention, threat-related, positive, and neutral word primes were presented parafoveally (2.2 degrees away from fixation) for 150 ms, under gaze-contingent foveal masking, to prevent eye fixations. The primes were followed by a probe word in a lexical-decision task. In Experiment 1, results showed a parafoveal threat-anxiety superiority: Parafoveal prime threat words facilitated responses to probe threat words for high-anxiety individuals, in comparison with neutral and positive words, and relative to low-anxiety individuals. This reveals an advantage in threat processing by covert attention, without differences in overt attention. However, anxiety was also associated with greater familiarity with threat words, and the parafoveal priming effects were significantly reduced when familiarity was covaried out. To further examine the role of word knowledge, in Experiment 2, vocabulary and word familiarity were equated for low- and high-anxiety groups. In these conditions, the parafoveal threat-anxiety advantage disappeared. This suggests that the enhanced covert-attention effect depends on familiarity with words.     

Not fixating at the line of text comes at a cost

Previous research on eye guidance in reading has investigated systematic tendencies with respect to horizontal fixation locations on letters within words and the relationship between fixation location in a word and the duration of the fixation. The present study investigates where readers place their eyes vertically on the line of text and how vertical fixation location is related to fixation duration. Analyses were based on a large corpus of eye movement recordings from single-sentence reading. The vertical preferred viewing location was found to be within the vertical extent of the font, but fixations beyond the vertical boundaries of the text also frequently occurred. Analyzing fixation duration as a function of vertical fixation location revealed a vertical optimal viewing position (vOVP) effect: Fixations were shortest when placed optimally on the line of text, and fixation duration gradually increased for fixations that fell above or below the line of text. The vOVP effect can be explained by the limits of visual resolution along the vertical meridian. It is concluded that vertical and horizontal landing positions in single-sentence reading are associated with differences in fixation durations in opposite ways.