Benjamin Wolfe

Facilitating recognition of crowded faces with presaccadic attention

In daily life, we make several saccades per second to objects we cannot normally recognize in the periphery due to visual crowding. While we are aware of the presence of these objects, we cannot identify them and may, at best, only know that an object is present at a particular location. The process of planning a saccade involves a presaccadic attentional component known to be critical for saccadic accuracy, but whether this or other presaccadic processes facilitate object identification as opposed to object detection—especially with high level natural objects like faces—is less clear. In the following experiments, we show that presaccadic information about a crowded face reduces the deleterious effect of crowding, facilitating discrimination of two emotional faces, even when the target face is never foveated. While accurate identification of crowded objects is possible in the absence of a saccade, accurate identification of a crowded object is considerably facilitated by presaccadic attention. Our results provide converging evidence for a selective increase in available information about high level objects, such as faces, at a presaccadic stage.

Saccadic remapping of object-selective information

Saccadic remapping, a presaccadic increase in neural activity when a saccade is about to bring an object into a neuron’s receptive field, may be crucial for our perception of a stable world. Studies of perception and saccadic remapping, like ours, focus on the presaccadic acquisition of information from the saccade target, with no direct reference to underlying physiology. While information is known to be acquired prior to a saccade, it is unclear whether object-selective or feature-specific information is remapped. To test this, we performed a series of psychophysical experiments in which we presented a peripheral, nonfoveated face as a presaccadic target. The target face disappeared at saccade onset. After making a saccade to the location of the peripheral target face (which was no longer visible), subjects misperceived the expression of a subsequent, foveally presented neutral face as being repelled away from the peripheral presaccadic face target. This effect was similar to a sequential shape contrast or negative aftereffect but required a saccade, because covert attention was not sufficient to generate the illusion. Additional experiments further revealed that inverting the faces disrupted the illusion, suggesting that presaccadic remapping is object-selective and not based on low-level features. Our results demonstrate that saccadic remapping can be an object-selective process, spatially tuned to the target of the saccade and distinct from covert attention in the absence of a saccade.

Visual motion shifts saccade targets

Saccades are made thousands of times a day and are the principal means of localizing objects in our environment. However, the saccade system faces the challenge of accurately localizing objects as they are constantly moving relative to the eye and head. Any delays in processing could cause errors in saccadic localization. To compensate for these delays, the saccade system might use one or more sources of information to predict future target locations, including changes in position of the object over time, or its motion. Another possibility is that motion influences the represented position of the object for saccadic targeting, without requiring an actual change in target position. We tested whether the saccade system can use motion-induced position shifts to update the represented spatial location of a saccade target, by using static drifting Gabor patches with either a soft or a hard aperture as saccade targets. In both conditions, the aperture always remained at a fixed retinal location. The soft aperture Gabor patch resulted in an illusory position shift, whereas the hard aperture stimulus maintained the motion signals but resulted in a smaller illusory position shift. Thus, motion energy and target location were equated, but a position shift was generated in only one condition. We measured saccadic localization of these targets and found that saccades were indeed shifted, but only with a soft-aperture Gabor patch. Our results suggest that motion shifts the programmed locations of saccade targets, and this remapped location guides saccadic localization.

Empirical Assessment of the Legibility of the Highway Gothic and Clearview Signage Fonts

Older drivers represent the fastest-growing segment of the driving population. Aging is associated with well-known declines in reaction time and visual processing, and, as such, future roadway infrastructure and related design considerations will need to accommodate this population. One potential area of concern is the legibility of highway signage. FHWA recently revoked an interim approval that allowed optional use of the Clearview typeface in place of the traditional Highway Gothic typeface for signage. The legibility of the two fonts was assessed with color combinations that maximized the contrast (positive or negative) or approximated a color configuration used in highway signage. Psychophysical techniques were used to establish thresholds for the time needed to decide accurately—under glancelike reading conditions—whether a string of letters was a word, as a proxy for legibility. These thresholds were lower for Clearview (indicating superior legibility) than for Highway Gothic across all conditions. Legibility thresholds were lowest for negative-contrast conditions and highest for positive-contrast conditions, with colored highway signs roughly between the two extremes. These thresholds also increased significantly across the age range studied. The method used to investigate the legibility of signage fonts adds methodological diversity to the literature along with evidence supporting the superior legibility of the Clearview font over Highway Gothic. The results do not suggest that the Clearview typeface is the optimal solution for all signage but they do indicate that additional scientific evaluations of signage legibility are warranted in different operating contexts.

Unifying Visual Space Across the Left and Right Hemifields

Visual space is perceived as continuous and stable even though visual inputs from the left and right visual fields are initially processed separately within the two cortical hemispheres. In the research reported here, we examined whether the visual system utilizes a dynamic recalibration mechanism to integrate these representations and to maintain alignment across the visual fields. Subjects adapted to randomly oriented moving lines that straddled the vertical meridian; these lines were vertically offset between the left and right hemifields. Subsequent vernier alignment judgments revealed a negative aftereffect: An offset in the same direction as the adaptation was required to correct the perceived misalignment. This aftereffect was specific to adaptation to vertical, but not horizontal, misalignments and also occurred following adaptation to movie clips and patterns without coherent motion. Our results demonstrate that the visual system unifies the left and right halves of visual space by continuously recalibrating the alignment of elements across the visual fields.

The effects of visual crowding, text size, and positional uncertainty on text legibility at a glance

Reading at a glance, once a relatively infrequent mode of reading, is becoming common. Mobile interaction paradigms increasingly dominate the way in which users obtain information about the world, which often requires reading at a glance, whether from a smartphone, wearable device, or in-vehicle interface. Recent research in these areas has shown that a number of factors can affect text legibility when words are briefly presented in isolation. Here we expand upon this work by examining how legibility is affected by more crowded presentations. Word arrays were combined with a lexical decision task, in which the size of the text elements and the inter-line spacing (leading) between individual items were manipulated to gauge their relative impacts on text legibility. In addition, a single-word presentation condition that randomized the location of presentation was compared with previous work that held position constant. Results show that larger text was more legible than smaller text. Wider leading significantly enhanced legibility as well, but contrary to expectations, wider leading did not fully counteract decrements in legibility at smaller text sizes. Single-word stimuli presented with random positioning were more difficult to read than stationary counterparts from earlier studies. Finally, crowded displays required much greater processing time compared to single-word displays. These results have implications for modern interface design, which often present interactions in the form of scrollable and/or selectable lists. The present findings are of practical interest to the wide community of graphic designers and interface engineers responsible for developing our interfaces of daily use.

Age-related differences in the legibility of degraded text

Aging-related changes in the visual system diminish the capacity to perceive the world with the ease and fidelity younger adults are accustomed to. Among many consequences of this, older adults find that text that they could once read easily proves difficult to read, even with sufficient acuity correction. Building on previous work examining visual factors in legibility, we examine potential causes for these age-related effects in the absence of other ocular pathology. We asked participants to discriminate words from non-words in a lexical decision task. The stimuli participants viewed were either blurred or presented in a noise field to simulate, respectively, decreased sensitivity to fine detail (loss of acuity) and detuning of visually selective neurons. We then use the differences in performance between older and younger participants to suggest how older participants’ performance could be approximated to facilitate maximally usable designs.

Dynamic recalibration of perceived space across the visual hemifields

Visual input from the left and right visual fields is initially processed separately in the two cortical hemispheres, yet the visual system integrates these representations into a single continuous percept of space. In order to represent alignment and symmetry across the visual field, the visual system may continually recalibrate visual information across the hemifields. If so, any differences, such as misalignments across the two hemifields, should be adaptable. To test this, observers adapted to a set of large randomly rotating and moving colored lines in a circular Gaussian contrast aperture on a dark background, while performing a target detection task at fixation. The stimulus was split across the vertical meridian such that the lines in the left hemifield were shifted 1.8º higher than the lines in the right hemifield, or vice versa. An occluder strip (3.5º wide) eliminated visibility of the discontinuity in the lines at the vertical meridian, and observers were tested in a dark room with neutral density filter goggles to eliminate visual references. After 8 minutes of initial adaptation, observers performed a Vernier discrimination task in which they judged the relative positions of two brief (83 ms) horizontal lines straddling the vertical meridian. Vernier judgments reflected a negative aftereffect; an average shift of 0.08º in the direction of adaptation was required to null the perceived misalignment (p = 0.006). We replicated this result with adaptation to natural movies with the left and right halves of the image vertically misaligned. Results showed that a Vernier offset of 0.07º in the direction of adaptation was necessary to cancel the perceived misalignment (p = 0.02). Our results indicate that the visual system computes and dynamically recalibrates the relative alignment of elements across the visual fields-a mechanism that would help achieve and maintain continuous and stable perception of space. Meeting abstract presented at VSS 2015.

Object-selective processing of remapped information.

Saccadic remapping may be an object-selective process (Wolfe and Whitney, VSS2014). Using the face aftereffect (FAE; Webster et al., 2004) in a saccadic paradigm, we showed that remapped information from a face that was never foveated could alter perception of a subsequently foveated face, suggesting that saccadic remapping may acquire object- rather than feature-level information. If remapping is object-selective, we reasoned that there should also be an inversion effect with our stimuli (Yin, 1969), and that our effect should be temporally tuned around the time of the saccade (Duhamel et al., 1992). In one experiment, we tested whether remapped face information exhibits an inversion effect. We presented an inverted emotional face (happy or sad) 15º from fixation and asked subjects to saccade to it; it was removed from the display on saccade onset. Once the saccade terminated, an inverted morphed test face (ranging from happy to sad) was presented foveally and subjects judged whether the test face was happy or sad. Using the method of constant stimuli, we estimated the point of subjective equality as a measure of the FAE. Compared to the same experiment performed with upright pre-saccadic faces, we found a significantly reduced saccade-contingent FAE with inverted faces. We performed a separate experiment to determine the temporal tuning of saccadic remapping relative to saccade onset. Subjects were cued to saccade to a peripheral location, where an emotional face was presented for 50 ms at a random temporal offset after the cue and before the saccade. Subjects then judged a morphed test face at fixation after the saccade. We find that information is only remapped from the pre-saccadic face when it is presented 120 ms or less prior to the saccade. These new results support our account that saccadic remapping is object-selective and occurs immediately prior to the saccade. Meeting abstract presented at VSS 2015.