Figure 1 - uploaded by Susana Martinez-Conde
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Demonstration of peripheral visual fading, or Troxler effect. Fixate precisely on the red spot, while paying attention to the bluish annulus. After a few seconds, the annulus will disappear, and the red spot will appear to be surrounded by a completely white field. Eye movement immediately brings the blue annulus back to perception. From MartinezConde S, Macknik SL, Hubel DH: The role of fixational eye movements in visual perception. Nat Rev Neurosci 5:229-240, 2004. Courtesy of Susana Martinez-Conde, PhD.
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... though perfect retinal stabi- lization is most easily achieved under laboratory conditions, objects fade in our visual periphery quite often in nor- mal vision. We are usually unaware of the process. Peripheral fading of sta- tionary objects was first noticed by Troxler in the early 1800s (Fig. 1). He reported that, under voluntary fixation, stationary objects in the periphery of vision tend to fade and disappear. 10 In the late 1950s, Clarke made a connec- tion between Troxler fading and the fading of stabilized images in the labo- ratory, and attributed both phenomena to neural adaptation. 2,3 The simplest explanation for ...
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... Even in the intervals between microsaccades, the eyes continue to move, making slower movements of comparable amplitude known as drifts. Superimposed on all these other movements, a low amplitude, high frequency tremor carries on continually [118,130,132,133]. 12 As already noted, although most of them are not made by conscious volition, saccades, including microsaccades are clearly under cognitive control, and serve important visual functions. ...
... 12 As already noted, although most of them are not made by conscious volition, saccades, including microsaccades are clearly under cognitive control, and serve important visual functions. The evidence is, as yet, less clear concerning drift and tremor, but there are good reasons to think that the same is also true of them [118,132,133,[135][136][137][138][139][140][141]. Indeed, counterintuitive as it may seem, "fixation eye movements" in general (microsaccades and/or drifts, and perhaps tremor too) seem to be necessary in order for us to make out fine levels of visual detail. ...
A theory of the structure and cognitive function of the human imagination that attempts to do justice to traditional intuitions about its psychological centrality is developed, largely through a detailed critique of the theory propounded by Colin McGinn. Like McGinn, I eschew the highly deflationary views of imagination, common amongst analytical philosophers, that treat it either as a conceptually incoherent notion, or as psychologically trivial. However, McGinn fails to develop his alternative account satisfactorily because (following Reid, Wittgenstein and Sartre) he draws an excessively sharp, qualitative distinction between imagination and perception, and because of his flawed, empirically ungrounded conception of hallucination. His arguments in defense of these views are rebutted in detail, and the traditional, passive, Cartesian view of visual perception, upon which several of them implicitly rely, is criticized in the light of findings from recent cognitive science and neuroscience. It is also argued that the apparent intuitiveness of the passive view of visual perception is a result of mere historical contingency. An understanding of perception (informed by modern visual science) as an inherently active process enables us to unify our accounts of perception, mental imagery, dreaming, hallucination, creativity, and other aspects of imagination within a single coherent theoretical framework.
... Measuring and reporting fixation durations is common practice in experimental psychology (e.g., Martinez-Conde, 2005;Martinez-Conde, Macknik, & Hubel, 2004;Nuthmann, Smith, Engbert, & Henderson, 2010;Tatler, Gilchrist, & Land, 2005). There is, in fact, a growing body of research that associates fixation durations with cognitive processes such as attention, information processing, memory, and anticipation (e.g., Castelhano & Henderson, 2008;Kowler, 2011;Malcolm & Henderson, 2010;Rayner, Smith, Malcolm, & Henderson, 2009;Richardson, Dale, & Spivey, 2007). ...
Fixation durations (FD) have been used widely as a measurement of information processing and attention. However, issues like data quality can seriously influence the accuracy of the fixation detection methods and, thus, affect the validity of our results (Holmqvist, Nyström, & Mulvey, 2012). This is crucial when studying special populations such as infants, where common issues with testing (e.g., high degree of movement, unreliable eye detection, low spatial precision) result in highly variable data quality and render existing FD detection approaches highly time consuming (hand-coding) or imprecise (automatic detection). To address this problem, we present GraFIX, a novel semiautomatic method consisting of a two-step process in which eye-tracking data is initially parsed by using velocity-based algorithms whose input parameters are adapted by the user and then manipulated using the graphical interface, allowing accurate and rapid adjustments of the algorithms' outcome. The present algorithms (1) smooth the raw data, (2) interpolate missing data points, and (3) apply a number of criteria to automatically evaluate and remove artifactual fixations. The input parameters (e.g., velocity threshold, interpolation latency) can be easily manually adapted to fit each participant. Furthermore, the present application includes visualization tools that facilitate the manual coding of fixations. We assessed this method by performing an intercoder reliability analysis in two groups of infants presenting low- and high-quality data and compared it with previous methods. Results revealed that our two-step approach with adaptable FD detection criteria gives rise to more reliable and stable measures in low- and high-quality data.
... When humans fixate, both foveae align with the object of interest with a steady gaze (Fig. 3b). When an object is static, human fixation is associated with a decrease in head movements and is fine-tuned with the eyes 'locked' on the target of attention (although the eyes still engage in very subtle movements; Martinez-Conde, 2005). A similar visual fixation strategy is present in other vertebrates such as dogs (Somppi, Tornqvist, Hanninen, Krause, & Vainio, 2012). ...
Sensitivity to the gaze of other individuals has long been a primary focus in sociocognitive research on humans and other animals. Information about where others are looking may often be of adaptive value in social interactions and predator avoidance, but studies across a range of taxa indicate there are substantial differences in the extent to which animals obtain and use information about other individuals' gaze direction. As the literature expands, it is becoming increasingly difficult to make comparisons across taxa as experiments adopt and adjust different methodologies to account for differences between species in their socioecology, sensory systems and possibly also their underlying cognitive mechanisms. Furthermore, as more species are found to exhibit gaze sensitivity, more terminology arises to describe the behaviours. To clarify the field, we propose a restricted nomenclature that defines gaze sensitivity in terms of observable behaviour, independent of the underlying mechanisms. This is particularly useful in nonhuman animal studies where cognitive interpretations are ambiguous. We then describe how socioecological factors may influence whether species will attend to gaze cues, and suggest links between ultimate factors and proximate mechanisms such as cognition and perception. In particular, we argue that variation in sensory systems, such as retinal specializations and the position of the eyes, will determine whether gaze cues (e.g. head movement) are perceivable during visual fixation. We end by making methodological recommendations on how to apply these variations in socioecology and visual systems to advance the field of gaze research.
