1,721,020 research outputs found
Selection of visual information for lightness judgements by eye movements
No full textWhen judging the lightness of objects, the visual system has to take into account many factors such as shading, scene geometry, occlusions or transparency. The problemthen is to estimate global lightness based on a number of local samples that differ in luminance. Here,we showthat eye fixations play a prominent role in this selection process. We explored a special case of transparency for which the visual system separates surface reflectance from interfering conditions to generate a layered image representation. Eye movements were recorded while the observers matched the lightness of the layered stimulus. We found that observers did focus their fixations on the target layer, and this sampling strategy affected their lightness perception. The effect of image segmentation on perceived lightness was highly correlated with the fixation strategy and was strongly affected whenwe manipulated it using a gaze-contingent display. Finally, we disrupted the segmentation process showing that it causally drives the selection strategy. Selection through eye fixations can so serve as a simple heuristic to estimate the target reflectance. © 2013 The Author(s) Published by the Royal Society. All rights reserved
An evaluation of different measures of color saturation
No full textWe investigated how well seven saturation measures defined in CIECAM02, HSV, DKL, LAB, LUV, and CIE 1931 xyY color spaces correspond to human perception of saturation. We used a paradigm that allowed us to measure the perceived saturation of several standard color stimuli in many different directions of color space. We implemented this paradigm at different levels of luminance and varied background luminance relative to the luminance of our color stimuli in order to ensure the generality of our approach. We found that varying background luminance changed the relative saturation of the standard colors. Raising the overall luminance level did not have such an effect. We compared the results of our measurements to the predictions of the seven saturation measures. All of the measures could predict our observers’ judgments of saturation reasonably well. The measures that are based on measurements of discrimination thresholds (LUV, LAB, CIECAM02) performed best on average. However, some of the perceptual effects induced by changing background luminance could not be predicted by any measure
Data pertaining to "An evaluation of different measures of color saturation"
No full textThese data sets pertain to the article
Schiller, F., Valsecchi, M., & Gegenfurtner, K. R. (2017). An evaluation of different measures of color saturation. Vision Research. doi: 10.1016/j.visres.2017.04.012.
A description of the data sets can be found in the ReadMe.pdf file. Please contact [email protected] if you have further questions
The speed and accuracy of material recognition in natural images
No full textWe studied the time course of material categorization in natural images relative to superordinate and basic-level object categorization, using a backward-masking paradigm. We manipulated several low-level features of the images-including luminance, contrast, and color-to assess their potential contributions. The results showed that the speed of material categorization was roughly comparable to the speed of basic-level object categorization, but slower than that of superordinate object categorization. The performance seemed to be crucially mediated by low-level factors, with color leading to a solid increase in performance for material categorization. At longer presentation durations, material categorization was less accurate than both types of object categorization. Taken together, our results show that material categorization can be as fast as basic-level object categorization, but is less accurate. © 2013 Psychonomic Society, Inc
Saccadic and smooth-pursuit eye movements during reading of drifting texts
No full textReading is a complex visuomotor behavior characterized by an alternation of fixations and saccadic eye movements. Despite the widespread use of drifting texts in various settings, very little is known about eye movements under these conditions. Here we investigated oculomotor behavior during reading of texts which were drifting horizontally or vertically at different speeds. Consistent with previous reports, drifting texts were read by an alternation of smooth-pursuit and saccadic eye movements. Detailed analysis revealed several interactions between smooth pursuit and saccades. On one side, the gain of smooth pursuit was increased after the execution of a saccade. On the other side, the peak velocity of saccades was reduced for the horizontally drifting text, in which saccades and pursuit were executed in opposite directions. In addition, we show that well-known findings from the reading of static texts extend to drifting text, such as the preferred viewing location, the inverted optimal viewing position, and the correlation between saccade amplitude and subsequent pursuit/fixation duration. In general, individual eye-movement parameters such as saccade amplitude and fixation/pursuit durations were correlated across self-paced reading of static text and time-constrained reading of static and drifting texts. These results show that findings from basic oculomotor research also apply to the reading of drifting texts. Similarly, basic reading principles apply to the reading of static and drifting texts in a similar way. This exemplifies the reading of drifting text as a visuomotor behavior which is influenced by low-level eye-movement control as well as by cognitive and linguistic processing. © 2013 ARVO
Prediction shapes peripheral appearance
Full text linkPeripheral perception is limited in terms of visual acuity, contrast sensitivity, and positional uncertainty. In the present study we used an image-manipulation algorithm (the Eidolon Factory) based on a formal description of the visual field as a tool to investigate how peripheral stimuli appear in the presence of such limitations. Observers were asked to match central and peripheral stimuli, both configurations of superimposed geometric shapes and patches of natural images, in terms of the parameters controlling the amplitude of the perturbation (reach) and the cross-scale similarity of the perturbation (coherence). We found that observers systematically tended to report the peripheral stimuli as having shorter reach and higher coherence. This means that their matches both were less distorted and had sharper edges relative to the actual stimulus. Overall, the results indicate that the way we see objects in our peripheral visual field is complemented by our assumptions about the way the same objects would appear if they were viewed foveally
Perceived numerosity is reduced in peripheral vision
Full text linkIn four experiments we investigated the perception of numerosity in the peripheral visual field. We found that the perceived numerosity of a peripheral cloud of dots was judged to be inferior to the one of a central cloud of dots, particularly when the dots were highly clustered. Blurring the stimuli accordingly to peripheral spatial frequency sensitivity did not abolish the effect and had little impact on numerosity judgments. In a dedicated control experiment we ruled out that the reduction in peripheral perceived numerosity is secondary to a reduction of perceived stimulus size. We suggest that visual crowding might be at the origin of the observed reduction in peripheral perceived numerosity, implying that numerosity could be partly estimated through the individuation of the elements populating the array. © 2013 ARVO
Saccadic suppression measured by steady-state visual evoked potentials
Full text link<p>Dataset related to the following publication:</p>
<p>Chen, J., Valsecchi, M. & Gegenfurtner, K.R. (2019). Saccadic suppression measured by steady-state visual evoked potentials. <em>Journal of Neurophysiology, DIO: 10.1152/jn.00712.2018</em></p>
<p>Please refer to "data description.txt" for details about the data. </p>
Steady-state visually evoked potentials reveal partial size constancy in early visual cortex
Full text linkOur visual system maintains a stable representation of object size when viewing distance, and thus retinal size, changes. Previous studies have revealed that the extent of an object's representation in V1 shows systematic deviations from strict retinotopy when the object is perceived to be at different distances. It remains unknown, however, to what degree V1 activity accounts for perceptual size constancy. We investigated the neural correlates of size-constancy using steady-state visually evoked potentials (SSVEP) known to originate in early visual cortex. Flickering stimuli of various sizes were placed at a viewing distance of 40 cm and stimuli twice as large were shown at 80 cm. Thus both sets of stimuli had identical retinal sizes. At a constant viewing distance, SSVEP amplitude increased as a function of increasing retinal size. Crucially, SSVEP was larger when stimuli of a given retinal size were presented at 80 cm compared with at 40 cm independent of flicker frequency. Experiments were repeated and extended in virtual reality. Our results agree with previous findings showing that V1 activity plays a role in size constancy. Furthermore, we estimated the degree of the neural correction for the SSVEP as being close to 50% of the perceptual size constancy. This was the case in all experiments, independent of the effectiveness of perceptual size constancy. We conclude that retinotopy in V1 does get quite massively adjusted by perceived size, but not to the same extent as perceptual judgments
Attention is allocated closely ahead of the target during smooth pursuit eye movements: evidence from EEG frequency tagging
Full text link<p>Dataset relative to the following publication:</p>
<p>Chen, J., Valsecchi, M. & Gegenfurtner, K.R. (2017). Attention is allocated closely ahead of the target during smooth pursuit eye movements: Evidence from EEG frequency tagging. <strong>Neuropsychologia</strong>, doi: 10.1016/j.neuropsychologia.2017.06.024.</p>
<p>Please refer to "data description.txt" in each experiment for details about the data. </p>
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