150 research outputs found

    Summation of two illusions of extent

    Get PDF

    Change blindness: eradication of gestalt strategies

    Get PDF
    Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

    Estimating the subjective perception of object size and position through brain imaging and psychophysics

    Get PDF
    Perception is subjective and context-dependent. Size and position perception are no exceptions. Studies have shown that apparent object size is represented by the retinotopic location of peak response in V1. Such representation is likely supported by a combination of V1 architecture and top-down driven retinotopic reorganisation. Are apparent object size and position encoded via a common mechanism? Using functional magnetic resonance imaging and a model-based reconstruction technique, the first part of this thesis sets out to test if retinotopic encoding of size percepts can be generalised to apparent position representation and whether neural signatures could be used to predict an individual’s perceptual experience. Here, I present evidence that static apparent position – induced by a dot-variant Muller-Lyer illusion – is represented retinotopically in V1. However, there is mixed evidence for retinotopic representation of motion-induced position shifts (e.g. curveball illusion) in early visual areas. My findings could be reconciled by assuming dual representation of veridical and percept-based information in early visual areas, which is consistent with the larger framework of predictive coding. The second part of the thesis sets out to compare different psychophysical methods for measuring size perception in the Ebbinghaus illusion. Consistent with the idea that psychophysical methods are not equally susceptible to cognitive factors, my experiments reveal a consistent discrepancy in illusion magnitude estimates between a traditional forced choice (2AFC) task and a novel perceptual matching (PM) task – a variant of a comparison-of-comparisons (CoC) task, a design widely seen as the gold standard in psychophysics. Further investigation reveals the difference was not driven by greater 2AFC susceptibility to cognitive factors, but a tendency for PM to skew illusion magnitude estimates towards the underlying stimulus distribution. I show that this dependency can be largely corrected using adaptive stimulus sampling

    Born free and equal?: on the ethical consistency of animal equality

    Get PDF
    This dissertation investigates the possibility of constructing a consistent ethical system that offers clear notions of equality and incorporates an animal ethic. The first part is more meta-ethical in nature, reflecting on notions such as moral intuitions, universalism, consistency and coherence. It demonstrates that moral illusions might exist and offers a method to discover such moral illusions. The second part turns to normative ethics, dealing with principles of welfare, justice and basic rights. It tackles problems ranging from population ethics to non-ideal theory. Finally, the third part moves to applied (animal) ethics, In analogy to optical illusions, I demonstrate that speciesism is not only a kind of prejudicial discrimination but also a moral illusion: an obstinate intuitive judgment that is inconsistent with a coherent system. The third part also tackles the predation problem and the sentience problem in animal ethics. The end result of this work is a pluralist principlist ethical system that can be captured in a metaphor of five moral fingers working together as the moral hand. This moral hand is a constructed, coherent ethical system of five universalized ethical principles based on strong moral intuitions. The thumb represents the principle of universalism, which is a basic ingredient of coherentism, and generates an anti-discrimination rule. The index finger symbolizes a consequentialist welfare ethic, based on the coherence of impartiality and empathy. The middle finger is the mere means principle of a deontological rights ethic: humans (and animals) have a right not to be used as merely means to someone else’s ends. This principle captures a lot of moral intuitions that pop up in famous dilemmas. A fourth principle, the ring finger, refers to the value of biodiversity and adopts some elements of carnism, the opposite of veganism as ideology. This fourth principle solves the predation problem and is coherent with some other moral intuitions. Finally, the little finger represents the principle of tolerated partiality which can be used in some final moral dilemmas. With these five fingers of ethics, we can grasp the moral problem of consuming animal products, and answer the question whether veganism is a moral duty

    The inversion, part-whole, and composite effects reflect distinct perceptual mechanisms with varied relationships to face recognition

    Get PDF
    Face recognition is thought to rely on specific mechanisms underlying a perceptual bias toward processing faces as undecomposable wholes. This face-specific "holistic processing" is commonly quantified using 3 measures: the inversion, part-whole, and composite effects. Consequently, many researchers assume that these 3 effects measure the same cognitive mechanism(s) and these mechanisms contribute to the wide range of individual differences seen in face recognition ability. We test these assumptions in a large sample (N = 282), with individual face recognition abilities measured by the well-validated Cambridge Face Perception Test. Our results provide little support for either assumption. The small to nonexistent correlations among inversion, part-whole, and composite effects (correlations between -.03 and .28) fail to support the first assumption. As for the second assumption, only the inversion effect moderately predicts face recognition (r = .42); face recognition was weakly correlated with the part-whole effect (r = .25) and not correlated with the composite effect (r = .04). We rule out multiple artifactual explanations for our results by using valid tasks that produce standard effects at the group level, demonstrating that our tasks exhibit psychometric properties suitable for individual differences studies, and demonstrating that other predicted correlations (e.g., between face perception measures) are robust. Our results show that inversion, part-whole, and composite effects reflect distinct perceptual mechanisms, and we argue against the use of the single, generic term holistic processing when referring to these effects. Our results also question the contribution of these mechanisms to individual differences in face recognition

    Sensory Substitution is Substitution

    Get PDF

    Is the Mind Massively Modular?

    Get PDF
    Articl
    corecore