Capacity bounds and estimates for the finite scatterers MIMO wireless channel

We consider the limits to the capacity of the multiple-input–multiple-output wireless channel as modeled by the finite scatterers channel model, a generic model of the multipath channel which accounts for each individual multipath component. We assume a normalization that allows for the array gain due to multiple receive antenna elements and, hence, can obtain meaningful limits as the number of elements tends to infinity. We show that the capacity is upper bounded by the capacity of an identity channel of dimension equal to the number of scatterers. Because this bound is not very tight, we also determine an estimate of the capacity as the number of transmit/receive elements tends to infinity which is asymptotically accurate

Signal detection for non-orthogonal space-time block coding over time-selective fading channels

In the case of non-quasi-static (i.e., time-selective fast fading) channels, which do exist in practice, the performance of the existing NO-STBC detectors can suffer from an irreducible error floor. To this end, this letter proposes a zero-forcing-based signal detector, which is not only computationally simple but also highly effective in mitigating the impact of channel variation on system performance

Signal detection for orthogonal space-time block coding over time-selective fading channels: A PIC approach for the G(i) systems

One major assumption in all orthogonal space-time block coding (O-STBC) schemes is that the channel remains static over the entire length of the codeword. However, time selective fading channels do exist, and in such case the conventional O-STBC detectors can suffer from a large error floor in the high signal-to-noise ratio (SNR) cases. This paper addresses such an issue by introducing a parallel interference cancellation (PIC) based detector for the G(i) coded systems (i = 3 and 4)

Different reaction-times for subitizing, estimation, and texture

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spatiotemporal filtering and motion illusions

We are perplexed by Clarke et al.'s (2013) criticisms on our recent contribution to Journal of Vision (Pooresmaeili, Cicchini, Morrone, & Burr, 2012). Our group has long championed the idea that perceptual processing of information can be anchored in a dynamic coordinate system that need not correspond to the instantaneous retinal representation. Our recent evidence shows that temporal duration (Burr, Tozzi, & Morrone, 2007; Morrone, Cicchini, & Burr, 2010), orientation (Zimmermann, Morrone, Fink, & Burr, 2013), motion (Melcher & Morrone, 2003; Turi & Burr, 2012) and saccadic error-correction (Zimmermann, Burr, & Morrone, 2011) are all processed to some extent in spatiotopic coordinates. Imaging studies reinforce these studies (d'Avossa et al., 2007; Crespi et al., 2011). Much earlier, we showed that the processing of smoothly moving objects was not anchored in instantaneous, retinotopic coordinates, but in the reference frame given by the trajectory of motion. There is an effective interpolation along the trajectory, so temporal offsets in spatially collinear stimuli causes them to appear spatially offset, corresponding to the physical reality of stimuli moving over large regions of space, behind occluders (Burr, 1979; Burr & Ross, 1979). Our explanation for this surprising effect was that it could be a direct consequence of the spatiotemporal orientation of the impulsive response of motion detectors, providing the spatiotemporal reference frame needed to account for the interactions between time and space (Burr & Ross, 1986; Burr, Ross, & Morrone, 1986; Burr & Ross, 2004; Nishida, 2004). Recently, we have applied the concept of spatiotemporal oriented receptive fields to account for ''predictive remapping,'' the ''nonretinotopic'' effects that occur on each saccadic eye-movement (Burr & Morrone, 2010; Burr & Morrone, 2012; Cicchini, Binda, Burr, & Morrone, 2012). We were most impressed by the compelling demonstrations of Herzog's group, clearly showing that the reference frame of processing is not the instantaneous retinal position, but is flexible, depending not only on real physical motion, but on an illusory apparent motion where the stimuli do not actually move (Boi, Ogmen, Krummenacher, Otto, & Herzog, 2009). This seemed to us important, worthy of quantitative measurement and modeling, particularly to see whether these new effects may fall within the framework that so successfully explained previous demonstrations, such as spatiotemporal interpolation. It is reassuring that Clarke et al. (2013) confirm our results, albeit with some variability between subjects. But more importantly add a very nice result in showing that our simplified version of the ''litmus test'' can be enhanced by attending to the motion. This is an excellent point that we overlooked. The strength of this type of motion is well known to depend on attention (Cavanagh, 1992), and it is indeed interesting that the strength of motion-induced effects depends not only on the physical conditions, but on internal states such as attention. Perhaps attention may also provide the flexibility in choosing the most appropriate scale for analysis, which in this case would be lower, given that attention is diverted to the periphery. This would add strength to our model, and an idea worth following up

Pupillometry correlates of visual priming, and their dependency on autistic traits

In paradigms of visual search where the search feature (say color) can change from trial to trials, responses are faster for trials where the search color is repeated than when it changes. This is a clear example of "priming" of attention. Here we test whether the priming effects can be revealed by pupillometry, and also whether they are related to autistic-like personality traits, as measured by the Autism-Spectrum Quotient (AQ). We repeated Maljkovic and Nakayama's (1994) classic priming experiment, asking subjects to identify rapidly the shape of a singleton target defined by color. As expected, reaction times were faster when target color repeated, and the effect accumulated over several trials; but the magnitude of the effect did not correlate with AQ. Reaction times were also faster when target position was repeated, again independent of AQ. Presentation of stimuli caused the pupil to dilate, and the magnitude of dilation was greater for switched than repeated trials. This effect did not accumulate over trials, and did not correlate with the reaction times difference, suggesting that the two indexes measure independent aspects of the priming phenomenon. Importantly, the amplitude of pupil modulation correlated negatively with AQ, and was significant only for those participants with low AQ. The results confirm that pupillometry can track perceptual and attentional processes, and furnish useful information unobtainable from standard psychophysics, including interesting dependencies on personality traits