Motion-detection thresholds for first- and second-order gratings and plaids

AbstractThe two-stage decomposition–recombination model of 2D motion perception has been criticised on the basis that the direction of plaid stimuli can be accurately discriminated at speeds so low that the direction of their Fourier components is not discriminable. The nature of this gap in performance between gratings and plaids was investigated across a range of spatial frequencies and durations for first- and second-order stimuli. Motion-detection thresholds were obtained using a 2AFC, constant stimuli procedure and it was found that although thresholds for detection of plaid motion were often lower than those for gratings, the gap in performance between first-order plaids and gratings was unreliable, varying in magnitude and occasionally direction with the spatial frequency of the stimulus, presentation duration and observer. Curiously, an analogous gap found between purely second-order gratings and second-order plaids was more reliable and stable. It has been suggested that the gap is the result of ‘local motion detectors’ or broadly tuned V1 cells. The data presented here suggest that second-order mechanisms are responsible for the gap and that first-order information may even disrupt it

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Perceived time is spatial frequency dependent

YesWe investigated whether changes in low-level image characteristics, in this case spatial frequency, were capable of generating a well-known expansion in the perceived duration of an infrequent “oddball” stimulus relative to a repeatedly-presented “standard” stimulus. Our standard and oddball stimuli were Gabor patches that differed from each other in spatial frequency by two octaves. All stimuli were equated for visibility. Rather than the expected “subjective time expansion” found in previous studies, we obtained an equal and opposite expansion or contraction of perceived time dependent upon the spatial frequency relationship of the standard and oddball stimulus. Subsequent experiments using equi-visible stimuli reveal that mid-range spatial frequencies (ca. 2 c/deg) are consistently perceived as having longer durations than low (0.5 c/deg) or high (8 c/deg) spatial frequencies, despite having the same physical duration. Rather than forming a fixed proportion of baseline duration, this bias is constant in additive terms and implicates systematic variations in visual persistence across spatial frequency. Our results have implications for the widely cited finding that auditory stimuli are judged to be longer in duration than visual stimuli.Wellcome Trust, UK, the Federation of Ophthalmic and Dispensing Opticians, UK, and the College of Optometrists, UK

Duration channels mediate human time perception

The task of deciding how long sensory events seem to last is one that the human nervous system appears to perform rapidly and, for sub-second intervals, seemingly without conscious effort. That these estimates can be performed within and between multiple sensory and motor domains suggest time perception forms one of the core, fundamental processes of our perception of the world around us. Given this significance, the current paucity in our understanding of how this process operates is surprising. One candidate mechanism for duration perception posits that duration may be mediated via a system of duration-selective ‘channels’, which are differentially activated depending on the match between afferent duration information and the channels' ‘preferred’ duration. However, this model awaits experimental validation. In the current study, we use the technique of sensory adaptation, and we present data that are well described by banks of duration channels that are limited in their bandwidth, sensory-specific, and appear to operate at a relatively early stage of visual and auditory sensory processing. Our results suggest that many of the computational principles the nervous system applies to coding visual spatial and auditory spectral information are common to its processing of temporal extent

The contribution of local mechanisms to the visual perception of global motion

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Altmetrics: A Practical Guide for Librarians, Researchers and Academics

Book review of Altmetrics: A Practical Guide for Librarians, Researchers and Academics, by Andy Tattersall, ed. London: Facet Publishing, 2016. 224p. $95.00 (ISBN 978-1-78330-010-5).2, O

Altmetrics: A Practical Guide for Librarians, Researchers and Academics

Book review of Altmetrics: A Practical Guide for Librarians, Researchers and Academics, by Andy Tattersall, ed. London: Facet Publishing, 2016. 224p. $95.00 (ISBN 978-1-78330-010-5).2, O

Selfish Memes: An Update of Richard Dawkins’ Bibliometric Analysis of Key Papers in Sociobiology

In the second edition of The Selfish Gene, Richard Dawkins included a short bibliometric analysis of key papers instrumental to the sociobiological revolution, the intention of which was to support his proposal that ideas spread within a population in an epidemiological manner. In his analysis, Dawkins primarily discussed the influence of an article by British evolutionary biologist William Donald Hamilton which had introduced the concept of “inclusive fitness”, and he argued that citations to it were accumulating in a very different manner to two other seminal papers, demonstrating the appearance and spread of a new “meme” in circles. This paper re-examines Dawkins’ original analysis and the conclusions drawn from it, and updates those conclusions based on citation data accumulated in the intervening three decades since . This updated analysis shows that patterns of citation for the three papers, and Dawkins’ book itself, are actually remarkably similar and show no qualitative difference in citation growth. The data are well described by a two-phase exponential model of citation growth in which citations accumulate rapidly and then saturate at a slower level of growth dictated primarily by the general increase in production. It is speculated that this two-phase exponential growth, with some modification to account for papers that are not immediately discovered, may be a signature that will help to reveal the emergence of genuinely novel ideas within the literature

The amblyopic deficit for global motion is spatial scale invariant

AbstractHumans with amblyopia display anomalous performance for global motion discrimination. Attempts have been made to rule out an explanation based solely on the visibility loss in lower visual areas. However, it remains a possibility that the altered scale over which local motion is processed in V1 might lead to reduced efficiency of global motion processing in extra-striate cortex. We use stimuli composed of spatial frequency bandpass elements, equated for visibility, to show that the global motion deficit in amblyopia for both fellow and amblyopic eyes is still present once impairments in low-level processing have been factored out. This residual deficit appears to be spatial scale invariant and the relative deficit between the eyes shows a dependence on stimulus speed. We believe that this rules out an explanation of the amblyopic global motion deficit based solely on local motion input. We suggest instead that, in addition to low-level deficits, motion processing in a broadband, extra-striate, global motion mechanism is impaired in amblyopia