Escher Chairs illusion

Nick Scott-Samuel, George Lovell, Hiroshi Ashida, and Sam published a (very) little article on the Stacking Chairs illusion in iPerception. This was all mainly Nick’s work who discovered that stacking those kinds of chairs produces a very confusing and seemingly geometrically impossible percept:

EscherChairs

Note, a reviewer didn’t like that we called this stimulus Escher Chairs but I will stubbornly continue calling them that. They are very Escherial. Or perhaps Penrosian would be more appropriate?

Scott-Samuel, NE, Ashida, H, Lovell, PG, Meese, TS, & Schwarzkopf, DS (2018). Stacking Chairs: Local Sense and Global Nonsense. i-Perception 9(1).

pRF study on illusory contours

We recently published a study in Scientific Reports using illusory contour and amodal completion (occlusion) stimuli to map population receptive fields in early visual cortex. The signals are very weak but they correspond spatially very well to normal retinotopic maps. We suspect that what these experiments were really mapping is spatially selective attention cued to the position of the mapping stimuli. We thank Rebecca Tyrwhitt-Drake who did the original experiments for her student research project.

de Haas B, & Schwarzkopf DS (2018). Spatially selective responses to Kanizsa and occlusion stimuli in human visual cortex. Scientific Reports 8: 611.

End of an era

Last photo of the lab before Sam’s move to New Zealand. I hope we can all meet again soon on the same spot of earth wherever it may be!

 

LabBeforeNZ

MAPS method for measuring perceptual biases

Nonie Finlayson published this article in the Journal of Vision in which we investigate the estimates of perceptual biases produced by our Multiple Alternatives Perceptual Search (MAPS) method. Here we compare these biases to those estimated by the traditional method of constant stimuli and also conducted an attentional cuing experiment (done by Andria Papageorgiou for her MSc research project) to test whether biases are influenced by spatially selective attention.

Finlayson, NJ, Papageorgiou A, & Schwarzkopf, DS (2017). A new method for mapping perceptual biases across visual space. Journal of Vision 17: 5.

 

Reliability of pRF measurements

Former MSc student Jelle van Dijk published a study in NeuroImage in which we quantify the test-retest reliability of population receptive field measurements by comparing mapping experiments separated by several weeks. We found that visual field positions are extremely reliable but second-order parameters, such as pRF size and cortical magnification factor, is far less reliable (although still well correlated across sessions). Control experiments further suggested that these findings do not critically depend on the carrier stimuli used for mapping – but that reliability is a lot better if comparing mapping experiments conducted within the same scanning session. This suggests that changes of the scanning environment over time (both in terms of the setup or the scanner itself) are the greatest source of noise limiting reliability.

van Dijk, JA, de Haas, B, Moutsiana, C, & Schwarzkopf, DS (2016). Intersession reliability of population receptive field estimates. NeuroImage 143: 293–303.

Kanizsa contours require awareness of inducers

Former MSc student Theodora Banica published an article in PLoS One in which we investigated whether Kanizsa (illusory) contours are generated and perceived when observers are unaware of the inducers. This follows up earlier conflicting reports on this question. We conducted attentional cuing experiments as well as direct discrimination experiments while in some trials the inducing shapes were masked from awareness. We found no evidence that observers perceive Kanizsa contours when they are unaware of inducers.

Banica, T, & Schwarzkopf, DS (2016). Induction of Kanizsa contours requires awareness of the inducing context. PLoS One 11(8): e0161177.

Linking size perception to pRFs

Christina Moutsiana and Benjamin de Haas published a study in Nature Communications in which we investigate perceptual biases for size judgements and their relationship to the spatial tuning of visual cortex (population receptive fields). We describe a model for how the visual system may infer object size from activation patterns in early visual areas. In this article we also present the our new psychophysical method for estimating perceptual biases across several visual field locations, Multiple Alternatives Perceptual Search (MAPS).

Moutsiana*, C, de Haas*, B, Papageorgiou, A, van Dijk, JA, Balraj, A, Greenwood, JA, & Schwarzkopf, DS (2016). Cortical idiosyncrasies predict the perception of object size. Nature Communications 7: 12110.

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