New paper in Vision Research

Barhoom, H., Joshi, M. R., & Schmidtmann, G. (2021). The effect of response biases on resolution thresholds of Sloan letters in central and paracentral vision. Vision Research, 187, 110–119. https://doi.org/10.1016/j.visres.2021.06.002 [PDF]

Sloan letters are one of the most commonly used optotypes in clinical practice. Sloan letters have different relative legibility which could be due to three factors: perceivability, response bias, and similarity. Similarities between Sloan letters are known to be the major source of errors in threshold determination. However, little is known about the effect of response biases on the resolution thresholds. The aim of the present study was to investigate the effect of response bias and similarity on resolution thresholds of Sloan letters in central and paracentral vision. Eight subjects with normal ocular health participated in this study. Using the method of constant stimuli, we measured resolution thresholds for the Sloan letters set at 0° (central) and ± 3° eccentricity along the vertical meridian of the visual field. We calculated thresholds from data pooled across the 10 Sloan letters (pooled threshold). For further analysis we also calculated thresholds for each of the 10 Sloan letters (individual threshold). Response biases and letter similarities were determined using Luce's choice model. Results showed statistically significant differences between the mean individual thresholds of Sloan letters at the central and the upper visual field, but not at the lower visual field. For equally-sized letters at pooled threshold, unlike letter similarity, response biases showed statistically significant correlations to the differences in individual thresholds at the central, upper and lower visual field locations. For equally legible letters at individual thresholds, response biases and similarities showed no significant correlations to the differences in individual thresholds at the central, the upper and the lower visual field locations. These results suggest that, for equally-sized letters at pooled threshold, the response biases may lead to an underestimation of the pooled threshold, i.e. an overestimation of visual acuity measurements when using Sloan letters.

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AuthorGunnar Schmidtmann
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AVA Christmas Meeting 2020 - Presentation

The influence of partial occlusion on shape recognition

Humans are able to recognize objects from their outlines, largely irrespective of perspective, position and scale. Previous studies have drawn different conclusions regarding the importance of specific features such as curvature maxima in shape recognition. Schmidtmann et al. (2015) demonstrated that if observers were asked to match a segmented shape, which contained only either convex, concave curvature maxima or intermediate segments for varying lengths, to one of two subsequently presented re-scaled and re-positioned whole-contour shapes, they performed significantly better for convexities compared to the other shape features. Surprisingly, performance for convexities was independent of the length of the segments. These results implied that closed planar shapes are encoded using the positions of convexities, rather than concavities or intermediate regions, and that a simple shape-template model could explain performance (Schmidtmann et al., 2015, Scientific Reports, 5, 17142.). 

In natural viewing conditions, however, objects are often partially occluded. To investigate the effect of partial occlusion, I employed the same paradigm and stimuli as previously (Schmidtmann et al. 2015), but occluded either 16.7%, 33% or 50% of the shape (i.e., only half the shape was visible in the 50% condition). 

Results show that performance for convex features is superior to the other shape features and independent of segment length, replicating previous data. More importantly, however, recognition performance is only significantly impaired when 50% of the shape is occluded. These results demonstrate the importance of shape convexities for shape encoding, and the flexibility of the visual system to deal with partially occluded shapes.

https://ava2020meeting.wordpress.com

Schmidtmann, G., The influence of partial occlusion on shape recognition, AVA X-MAS Meeting 2020 [SLIDES]

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AuthorGunnar Schmidtmann
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New paper in i-Perception

In the blink of an eye: Reading mental states from briefly presented eye regions. 

Faces provide not only cues to an individual's identity, age, gender, and ethnicity but also insight into their mental states. The aim was to investigate the temporal aspects of processing of facial expressions of complex mental states for very short presentation times ranging from 12.5 to 100 ms in a four-alternative forced choice paradigm based on Reading the Mind in the Eyes test. Results show that participants are able to recognise very subtle differences between facial expressions ; performance is better than chance, even for the shortest presentation time. Importantly, we show for the first time that observers can recognise these expressions based on information contained in the eye region only. These results support the hypothesis that the eye region plays a particularly important role in social interactions and that the expressions in the eyes are a rich source of information about other peoples’ mental states. When asked to what extent the observers guessed during the task, they significantly underestimated their ability to make correct decisions, yet perform better than chance, even for very brief presentation times. These results are particularly relevant in the light of the current COVID-19 pandemic and the associated wearing of face coverings.

Schmidtmann, G., Logan, A. J., Carbon, C. C., Loong, J. T., Gold, I. (2020). In the blink of an eye: Reading mental states from briefly presented eye regions. i-Perception, 11(5), 1–18. [PDF]

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AuthorGunnar Schmidtmann
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New paper in i-Perception

In the blink of an eye: Reading mental states from briefly presented eye regions. 

Schmidtmann, G., Logan, A. J., Carbon, C. C., Loong, J. T., Gold, I. (2020). In the blink of an eye: Reading mental states from briefly presented eye regions. i-Perception, 11(5), 1–18. [PDF]

Faces provide not only cues to an individual's identity, age, gender, and ethnicity but also insight into their mental states. The aim was to investigate the temporal aspects of processing of facial expressions of complex mental states for very short presentation times ranging from 12.5 to 100 ms in a four-alternative forced choice paradigm based on Reading the Mind in the Eyes test. Results show that participants are able to recognise very subtle differences between facial expressions ; performance is better than chance, even for the shortest presentation time. Importantly, we show for the first time that observers can recognise these expressions based on information contained in the eye region only. These results support the hypothesis that the eye region plays a particularly important role in social interactions and that the expressions in the eyes are a rich source of information about other peoples’ mental states. When asked to what extent the observers guessed during the task, they significantly underestimated their ability to make correct decisions, yet perform better than chance, even for very brief presentation times. These results are particularly relevant in the light of the current COVID-19 pandemic and the associated wearing of face coverings.

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AuthorGunnar Schmidtmann
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