Linking individual differences in human V1 to perception around the visual field

A central question in neuroscience is how the organization of cortical maps relates to perception, for which human primary visual cortex (V1) is an ideal model system. V1 nonuniformly samples the retinal image, with greater cortical magnification (surface area per degree of visual field) at the fovea than periphery, and at the horizontal than vertical meridian. Moreover, the size and organization of V1 differs greatly across individuals. Here, we used fMRI and psychophysics in the same individuals to quantify individual differences in V1 cortical magnification and perceptual contrast sensitivity at the four polar angle meridians. Across individuals, the overall size of V1 and localized cortical magnification both positively correlated with contrast sensitivity. Moreover, increases in cortical magnification and contrast sensitivity at the horizontal compared to the vertical meridian were strongly correlated. These data reveal a tight link between cortical anatomy and visual perception at the level of individual observer and stimulus location.

Dependence of perceptual saccadic suppression on peri-saccadic image flow properties and luminance contrast polarity

Across saccades, perceptual detectability of brief visual stimuli is strongly diminished. We recently observed that this perceptual suppression phenomenon is jumpstarted in the retina, suggesting that the phenomenon might be significantly more visual in nature than normally acknowledged. Here, we explicitly compared saccadic suppression strength when saccades were made across a uniform image of constant luminance versus when saccades were made across image patches of different luminance, width, and trans-saccadic luminance polarity. We measured perceptual contrast thresholds of human subjects for brief peri-saccadic flashes of positive (luminance increments) or negative (luminance decrements) polarity. Perceptual thresholds were >6-7 times higher when saccades translated a luminance stripe or edge across the retina than when saccades were made over a completely uniform image patch. Critically, both background luminance and flash luminance polarity relative to the background strongly modulated peri-saccadic contrast thresholds. In addition, all of these very same visual dependencies also occurred in the absence of any saccades, but with qualitatively similar rapid translations of image patches across the retina. Our results support the notion that perceptual saccadic suppression may be fundamentally a visual phenomenon, and they motivate neurophysiological and theoretical investigations on the role of saccadic eye movement commands in modulating its properties.

Contrast perception as a visual heuristic in the formulation of referential expressions

We hypothesize that contrast perception works as a visual heuristic, such that when speakers perceive a significant degree of contrast in a visual display, they tend to produce the corresponding adjective to describe a referent. We tested this hypothesis in four language-production experiments. Experiment 1 revealed that speakers overspecify color adjectives in polychrome displays, whereas in monochrome displays they overspecified those properties that were contrastive, supporting the contrast perception hypothesis. Experiment 2 further supported our hypothesis by revealing an increase in color overspecification in monochrome displays when multicolored fillers were interspersed. Experiment 3 revealed that even atypical colors (which are overspecified more often than typical colors) are only mentioned in polychrome displays. In Experiment 4, participants named a target color faster in monochrome than in polychrome displays, suggesting that the tendency to overspecify color in polychrome displays is not a bottom-up effect, but a learned communicative strategy. These results support the view that perceptual contrast works as a visual heuristic for efficient communication.

Colour maps for fisheries acoustic echograms

Echograms are used to visualize fisheries acoustic data, but choice of colour map has a significant effect on appearance. Quantitative echograms should use colour maps, which are colourful (have a perceived variety and intensity of colours), sequential (have monotonic lightness), and perceptually uniform (have consistency of perceived colour contrast over their range). We measure whether colour maps are colourful (M^(3)>0), sequential (rs=±1), and perceptually uniform (ρ = 1) using an approximately perceptually uniform colour space (CIELAB). Whilst all the fisheries acoustic colour maps tested are colourful, none is sequential or perceptually uniform. The widely used EK500 colour map is extremely colourful (M^(3)=186), not sequential (rs=0.06), and has highly uneven perceptual contrast over its range (ρ=0.26). Of the fisheries acoustic colour maps tested, the Large Scale Survey System default colour map is least colourful (M^(3)=79), but comes closest to being sequential (rs=−0.94), and perceptually uniform (ρ=0.95). Modern colour maps have been specifically designed for colour contrast consistency, accessibility for viewers with red-green colour-blindness, and legibility when printed in monochrome, and may be better suited to the presentation and interpretation of quantitative fisheries acoustic echograms.

Contrast enhancement as motivation for closed syllable laxing and open syllable tensing

This paper proposes that closed syllable laxing and open syllable tensing of non-low vowels are motivated by conflicting strategies of contrast enhancement in vowel–consonant sequences. Laxing enhances the distinctiveness of consonant contrasts by allowing for more distinct VC formant transitions, in particular in sequences involving a non-low vowel followed by an oral labial/coronal/velar consonant (e.g. [p t k]). Tensing enhances the distinctiveness of vowel contrasts by providing more distinct formant realisations for vowels. Linguistic variation results from different ways of resolving the tension between maximising vowel dispersion and maximising consonant dispersion. Laxing typically applies before coda consonants as a way to compensate for the absence of good perceptual cues to place of articulation. The hypothesis that laxing enhances the distinctiveness of postvocalic place contrasts is supported by a study of mid-vowel laxing in French, which corroborates the general claim that perceptual contrast plays a role in shaping phonotactic restrictions.

Generalization of Classic Question Order Effects Across Cultures

Questionnaire design is routinely guided by classic experiments on question form, wording, and context conducted decades ago. This article explores whether two question order effects (one due to the norm of evenhandedness and the other due to subtraction or perceptual contrast) appear in surveys of probability samples in the United States and 11 other countries (Canada, Denmark, Germany, Iceland, Japan, the Netherlands, Norway, Portugal, Sweden, Taiwan, and the United Kingdom; N = 25,640). Advancing theory of question order effects, we propose necessary conditions for each effect to occur, and found that the effects occurred in the nations where these necessary conditions were met. Surprisingly, the abortion question order effect even appeared in some countries in which the necessary condition was not met, suggesting that the question order effect there (and perhaps elsewhere) was not due to subtraction or perceptual contrast. The question order effects were not moderated by education. The strength of the effect due to the norm of evenhandedness was correlated with various cultural characteristics of the nations. Strong support was observed for the form-resistant correlation hypothesis.