24,261 research outputs found

    Egocentric Reference Frame Bias In The Palmar Haptic Perception Of Surface Orientation

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    The effect of egocentric reference frames on palmar haptic perception of orientation was investigated in vertically separated locations in a sagittal plane. Reference stimuli to be haptically matched were presented either haptically (to the contralateral hand) or visually. As in prior investigations of haptic orientation perception, a strong egocentric bias was found, such that haptic orientation matches made in the lower part of personal space were much lower (i.e., were perceived as being higher) than those made at eye level. The same haptic bias was observed both when the reference surface to be matched was observed visually and when bimanual matching was used. These findings support the conclusion that, despite the presence of an unambiguous allocentric (gravitational) reference frame in vertical planes, haptic orientation perception in the sagittal plane reflects an egocentric bias

    Genus two mutant knots with the same dimension in knot Floer and Khovanov homologies

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    We exhibit an infinite family of knots with isomorphic knot Heegaard Floer homology. Each knot in this infinite family admits a nontrivial genus two mutant which shares the same total dimension in both knot Floer homology and Khovanov homology. Each knot is distinguished from its genus two mutant by both knot Floer homology and Khovanov homology as bigraded groups. Additionally, for both knot Heegaard Floer homology and Khovanov homology, the genus two mutation interchanges the groups in δ\delta-gradings kk and −k-k.Comment: Information about δ\delta-graded homology has been changed along with statement of Theorem 1 and Table 1. Significant changes to Section

    Surgery on links of linking number zero and the Heegaard Floer dd-invariant

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    We study Heegaard Floer homology and various related invariants (such as the hh-function) for two-component L-space links with linking number zero. For such links, we explicitly describe the relationship between the hh-function, the Sato-Levine invariant and the Casson invariant. We give a formula for the Heegaard Floer dd-invariants of integral surgeries on two-component L-space links of linking number zero in terms of the hh-function, generalizing a formula of Ni and Wu. As a consequence, for such links with unknotted components, we characterize L-space surgery slopes in terms of the ν+\nu^{+}-invariants of the knots obtained from blowing down the components. We give a proof of a skein inequality for the dd-invariants of +1+1 surgeries along linking number zero links that differ by a crossing change. We also describe bounds on the smooth four-genus of links in terms of the hh-function, expanding on previous work of the second author, and use these bounds to calculate the four-genus in several examples of links.Comment: This version accepted for publication in Quantum Topolog
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