Readout from iconic memory involves similar neural processes as selective spatial attention

Iconic memory and spatial attention are often considered as distinct topics, but may have functional similarities. Here we provide fMRI evidence for some common underlying neural effects. Participants judged three visual stimuli in one hemifield of a bilateral array comprising six stimuli. The relevant hemifield for partial report was indicated by an auditory cue, administered either before the visual array (pre-cues, spatial attention) or shortly after (post-cues, iconic memory). Pre- and post-cues led to similar activity modulations in lateral occipital cortex, contralateral to the cued side, indicating that readout from iconic memory can have similar neural effects to spatial attention. We also found common bilateral activation of a fronto-parietal network for post-cue and pre-cue trials. These neuroimaging data suggest that some common neural mechanisms underlie selective spatial attention and readout from iconic memory. Some differences were also found, with post-cues leading to higher activity in right middle frontal gyrus

Attentional load and sensory competition in human vision: Modulation of fMRI responses by load fixation during task-irrelevant stimulation in the peripheral visual field.

Perceptual suppression of distractors may depend on both endogenous and exogenous factors, such as attentional load of the current task and sensory competition among simultaneous stimuli, respectively. We used functional magnetic resonance imaging (fMRI) to compare these two types of attentional effects and examine how they may interact in the human brain. We varied the attentional load of a visual monitoring task performed on a rapid stream at central fixation without altering the central stimuli themselves, while measuring the impact on fMRI responses to task-irrelevant peripheral checkerboards presented either unilaterally or bilaterally. Activations in visual cortex for irrelevant peripheral stimulation decreased with increasing attentional load at fixation. This relative decrease was present even in V1, but became larger for successive visual areas through to V4. Decreases in activation for contralateral peripheral checkerboards due to higher central load were more pronounced within retinotopic cortex corresponding to 'inner' peripheral locations relatively near the central targets than for more eccentric 'outer' locations, demonstrating a predominant suppression of nearby surround rather than strict 'tunnel vision' during higher task load at central fixation. Contralateral activations for peripheral stimulation in one hemifield were reduced by competition with concurrent stimulation in the other hemifield only in inferior parietal cortex, not in retinotopic areas of occipital visual cortex. In addition, central attentional load interacted with competition due to bilateral versus unilateral peripheral stimuli specifically in posterior parietal and fusiform regions. These results reveal that task-dependent attentional load, and interhemifield stimulus-competition, can produce distinct influences on the neural responses to peripheral visual stimuli within the human visual system. These distinct mechanisms in selective visual processing may be integrated within posterior parietal areas, rather than earlier occipital cortex

Exploring How Industrial Designers Can Contribute to Scientific Research

This paper describes the initial findings of an empirical study exploring how industrial designers might be able to support scientists in their research activities. The paper compares and contrasts the findings of a literature review, a series of interviews with scientists and three case studies in which designers collaborated with scientific teams at a university. It reflects on the designers’ contribution to research and highlights potential barriers and enablers to collaboration. In addition to the expected contribution of designers to supporting commercialisation of technology, the research demonstrated the potential for industrial design to have an impact on research itself. When involved earlier in the scientific research process, designers can challenge the research direction and support scientists in demonstrating, communicating and exploring potential future applications

An earth pole-sitter using hybrid propulsion

In this paper we investigate optimal pole-sitter orbits using hybrid solar sail and solar electric propulsion (SEP). A pole-sitter is a spacecraft that is constantly above one of the Earth's poles, by means of a continuous thrust. Optimal orbits, that minimize propellant mass consumption, are found both through a shape-based approach, and solving an optimal control problem, using a direct method based on pseudo-spectral techniques. Both the pure SEP case and the hybrid case are investigated and compared. It is found that the hybrid spacecraft allows consistent savings on propellant mass fraction. Finally, is it shown that for sufficiently long missions (more than 8 years), a hybrid spacecraft, based on mid-term technology, enables a consistent reduction in the launch mass for a given payload, with respect to a pure SEP spacecraft

Morphological number-count and redshift distributions to I < 26 from the Hubble Deep Field: Implications for the evolution of Ellipticals, Spirals and Irregulars

We combine the photometric redshift data of Fernandez-Soto et al. (1997) with the morphological data of Odewahn et al. (1996) for all galaxies with I < 26.0 detected in the Hubble Deep Field. From this combined catalog we generate the morphological galaxy number-counts and corresponding redshift distributions and compare these to the predictions of high normalization zero- and passive- evolution models. From this comparison we conclude the following: (1) E/S0s are seen in numbers and over a redshift range consistent with zero- or minimal passive- evolution to I = 24. Beyond this limit fewer E/S0s are observed than predicted implying a net negative evolutionary process --- luminosity dimming, disassembly or masking by dust --- at I > 24. (2) Spiral galaxies are present in numbers consistent with zero- evolution predictions to I = 22. Beyond this magnitude some net- positive evolution is required. Although the number-counts are consistent with the passive-evolution predictions to I=26.0 the redshift distributions favor number AND luminosity evolution. (3) There is no obvious explanation for the late-type/irregular class and this category requires further subdivision. While a small fraction of the population lies at low redshift (i.e. true irregulars), the majority lie at redshifts, 1 < z < 3. At z > 1.5 mergers are frequent and, taken in conjunction with the absence of normal spirals at z > 2, the logical inference is that they represent the progenitors of normal spirals forming via hierarchical merging.Comment: Accepted for publication in ApJ Letters, colour plates available from http://www.phys.unsw.edu.au/~spd/bib.htm

Strong asymptotics for Jacobi polynomials with varying nonstandard parameters

Strong asymptotics on the whole complex plane of a sequence of monic Jacobi polynomials $P_n^{(\alpha_n, \beta_n)}$ is studied, assuming that $$\lim_{n\to\infty} \frac{\alpha_n}{n}=A, \qquad \lim_{n\to\infty} \frac{\beta _n}{n}=B,$$ with $A$ and $B$ satisfying $A > -1$, $B>-1$, $A+B < -1$. The asymptotic analysis is based on the non-Hermitian orthogonality of these polynomials, and uses the Deift/Zhou steepest descent analysis for matrix Riemann-Hilbert problems. As a corollary, asymptotic zero behavior is derived. We show that in a generic case the zeros distribute on the set of critical trajectories $\Gamma$ of a certain quadratic differential according to the equilibrium measure on $\Gamma$ in an external field. However, when either $\alpha_n$, $\beta_n$ or $\alpha_n+\beta_n$ are geometrically close to $\Z$, part of the zeros accumulate along a different trajectory of the same quadratic differential.Comment: 31 pages, 12 figures. Some references added. To appear in Journal D'Analyse Mathematiqu

Hemispheric differences in frontal and parietal influences on human occipital cortex: direct confirmation with concurrent TMS-fMRI

We used concurrent TMS-fMRI to test directly for hemispheric differences in causal influences of the right or left fronto-parietal cortex on activity (BOLD signal) in the human occipital cortex. Clinical data and some behavioral TMS studies have been taken to suggest right-hemisphere specialization for top-down modulation of vision in humans, based on deficits such as spatial neglect or extinction in lesioned patients, or findings that TMS to right (vs. left) fronto-parietal structures can elicit stronger effects on visual performance. But prior to the recent advent of concurrent TMS and neuroimaging, it was not possible to directly examine the causal impact of one (stimulated) brain region upon others in humans. Here we stimulated the frontal or intraparietal cortex in the left or right hemisphere with TMS, inside an MR scanner, while measuring with fMRI any resulting BOLD signal changes in visual areas V1-V4 and V5/MT+. For both frontal and parietal stimulation, we found clear differences between effects of right- versus left-hemisphere TMS on activity in the visual cortex, with all differences significant in direct statistical comparisons. Frontal TMS over either hemisphere elicited similar BOLD decreases for central visual field representations in V1-V4, but only right frontal TMS led to BOLD increases for peripheral field representations in these regions. Hemispheric differences for effects of parietal TMS were even more marked: Right parietal TMS led to strong BOLD changes in V1-V4 and V5/MT+, but left parietal TMS did not. These data directly confirm that the human frontal and parietal cortex show right-hemisphere specialization for causal influences on the visual cortex

Two-phase galaxy evolution: the cosmic star formation histories of spheroids and discs

From two very simple axioms: (1) that active galactic nucleus activity traces spheroid formation, and (2) that the cosmic star formation history is dominated by spheroid formation at high redshift, we derive simple expressions for the star formation histories of spheroids and discs, and their implied metal enrichment histories. Adopting a Baldry–Glazebrook initial mass function we use these relations and apply PEGASE.2 to predict the z = 0 cosmic spectral energy distributions (CSEDs) of spheroids and discs. The model predictions compare favourably to the dust-corrected CSED recently reported by the Galaxy And Mass Assembly team from the far-ultraviolet through to the K band. The model also provides a reasonable fit to the total stellar mass contained within spheroid and disc structures as recently reported by the Millennium Galaxy Catalogue team. Three interesting inferences can be made following our axioms: (1) there is a transition redshift at z ≈ 1.7 at which point the Universe switches from what we refer to as ‘hot mode evolution’ (i.e. spheroid formation/growth via mergers and/or collapse) to what we term ‘cold mode evolution’ (i.e. disc formation/growth via gas infall and minor mergers); (2) there is little or no need for any pre-enrichment prior to the main phase of star formation; (3) in the present Universe mass loss is fairly evenly balanced with star formation holding the integrated stellar mass density close to a constant value. The model provides a simple prediction of the energy output from spheroid and disc projenitors, the build-up of spheroid and disc mass and the mean metallicity enrichment of the Universe