Encoding Strategies Research Articles

Phase angle encoded upconversion luminescent nanocrystals for multiplexing applications.

Lanthanide-doped upconversion nanoparticles (UCNPs) are increasingly used as luminescent candidates in multiplexing applications due to their excellent optical properties. In the past, several encoding identities have been proposed for UCNPs, including emission colour, intensity ratio between different emission bands, colour spatial distribution, and luminescence lifetime. In this paper, a new optical encoding dimension for upconversion nanomaterials is developed by exploring their luminescence kinetics, i.e., the phase angle of upconversion luminescence in response to a harmonic-wave excitation. Our theoretical derivation shows that the phase angle is governed jointly by the rise and decay times, characterizing the upconversion luminescence kinetics. Experimentally, a full set of methods are developed to manage the upconversion luminescence kinetics, through which the rise and decay times can be manipulated dependently or independently. Furthermore, a large phase-angle space is achieved in which tens of unique codes can potentially be generated in the same colour channel. Our work greatly extends the multiplexing capacity of UCNPs, and offers new opportunities for their applications in a wide range such as microarray assays, bioimaging, anti-counterfeiting, deep tissue multiplexing labelling/detection and high-density data storage. In addition, the development of this luminescence kinetics-based optical encoding strategy is also instructive for developing multiplexing techniques using other cascade luminescent systems that inherently lack multi-spectral channels, such as triplet-triplet annihilation molecule pairs.

Secrecy in MIMO Networks with No Eavesdropper CSIT

We consider two fundamental multi-user channel models: the multiple-input multiple-output (MIMO) wiretap channel with one helper (WTH) and the MIMO multiple access wiretap (MAC-WT) channel. In each case, the eavesdropper has $K$ antennas while the remaining terminals have $N$ antennas each. We consider a fast fading channel where the channel state information (CSI) of the legitimate receiver is available at the transmitters but no CSI at the transmitters (CSIT) is available for the eavesdropper’s channel. We determine the optimal sum secure degrees of freedom (s.d.o.f.) for each channel model for the regime $K\leq N$ , and show that in this regime, the MAC-WT channel reduces to the WTH in the absence of eavesdropper CSIT. For the regime $N\leq K\leq 2N$ , we obtain the optimal linear s.d.o.f., and show that the MAC-WT channel and the WTH have the same optimal s.d.o.f. when restricted to linear encoding strategies. In the absence of any such restrictions, we provide an upper bound for the sum s.d.o.f. of the MAC-WT channel in the regime $N\leq K\leq 2N$ . Our results show that unlike in the single-input single-output case, there is loss of s.d.o.f. for even the WTH due to lack of eavesdropper CSIT when $K\geq N$ .

MISO Broadcast Channel With Hybrid CSIT: Beyond Two Users

We study the impact of heterogeneity of channel-state-information available at the transmitters (CSIT) on the capacity of broadcast channels with a multiple-antenna transmitter and $k$ single-antenna receivers (MISO BC). In particular, we consider the $k$-user MISO BC, where the CSIT with respect to each receiver can be either instantaneous/perfect, delayed, or not available; and we study the impact of this heterogeneity of CSIT on the degrees-of-freedom (DoF) of such network. We first focus on the $3$-user MISO BC; and we completely characterize the DoF region for all possible heterogeneous CSIT configurations, assuming linear encoding strategies at the transmitters. The result shows that the state-of-the-art achievable schemes in the literature are indeed sum-DoF optimal, when restricted to linear encoding schemes. To prove the result, we develop a novel bound, called Interference Decomposition Bound, which provides a lower bound on the interference dimension at a receiver which supplies delayed CSIT based on the average dimension of constituents of that interference, thereby decomposing the interference into its individual components. Furthermore, we extend our outer bound on the DoF region to the general $k$-user MISO BC, and demonstrate that it leads to an approximate characterization of linear sum-DoF to within an additive gap of $0.5$ for a broad range of CSIT configurations. Moreover, for the special case where only one receiver supplies delayed CSIT, we completely characterize the linear sum-DoF.

Reversible data hiding in dual stego-images using frequency-based encoding strategy

Reversible data hiding methods can embed secret data into multimedia to prevent attacks from hackers. Reversible data hiding methods based on multiple stego-images have been proposed extensively in...

Spatial Mnemonic Encoding: Theta Power Decreases and Medial Temporal Lobe BOLD Increases Co-Occur during the Usage of the Method of Loci.

The method of loci is one, if not the most, efficient mnemonic encoding strategy. This spatial mnemonic combines the core cognitive processes commonly linked to medial temporal lobe (MTL) activity: spatial and associative memory processes. During such processes, fMRI studies consistently demonstrate MTL activity, while electrophysiological studies have emphasized the important role of theta oscillations (3–8 Hz) in the MTL. However, it is still unknown whether increases or decreases in theta power co-occur with increased BOLD signal in the MTL during memory encoding. To investigate this question, we recorded EEG and fMRI separately, while human participants used the spatial method of loci or the pegword method, a similarly associative but nonspatial mnemonic. The more effective spatial mnemonic induced a pronounced theta power decrease source localized to the left MTL compared with the nonspatial associative mnemonic strategy. This effect was mirrored by BOLD signal increases in the MTL. Successful encoding, irrespective of the strategy used, elicited decreases in left temporal theta power and increases in MTL BOLD activity. This pattern of results suggests a negative relationship between theta power and BOLD signal changes in the MTL during memory encoding and spatial processing. The findings extend the well known negative relation of alpha/beta oscillations and BOLD signals in the cortex to theta oscillations in the MTL.

A Functional Role for Neural Columns: Resolving F2 Transition Variability in Stop Place Categorization

Documented examples from neuroethology have revealed species-specific neural encoding mechanisms capable of mapping highly variable, but lawful, visual and auditory inputs within neural columns. By virtue of the entire column being the functional unit of both representation and processing, signal variation is collectively ‘absorbed’, and hence normalized, to help form natural categories possessing an underlying physically-based commonality. Stimulus-specific ‘tolerance ranges’ define the limits of signal variation, effectively shaping the functionality of the columnar-based processing. A conceptualization for an analogous human model utilizing this evolutionarily conserved neural encoding strategy for signal variability absorption is described for the non-invariance issue in stop place perception.

The roles of encoding strategies and retrieval practice in test-expectancy effects

ABSTRACTWe investigated whether expectations for different kinds of memory tests induce qualitatively different encoding strategies. In Experiment 1, participants studied four lists of words and after each list completed a cued-recall test that contained either all semantic or all orthographic cues so as to build up an expectancy for receiving the same type of test for the fifth critical study list. To rule out that the test-expectancy effects in Experiment 1 were due to differences in retrieval practice, in Experiment 2, participants received three practice tests each for both cue-types. Participants’ test expectancy for all lists was induced by telling them before each list the type of cue they would receive for the upcoming study list. In both experiments, the critical test contained both expected and unexpected cues. In Experiment 1, participants who expected semantic cues had better recall to the semantic cues than to the orthographic cues and vice versa for those who expected orthographic cues. However, in Experiment 2, there was no effect of test expectancy. These findings suggest that the test-expectancy effects in Experiment 1 were due to more retrieval practice on the expected than unexpected tests rather than to qualitatively different test-expectancy-induced encoding strategies.

Production does not improve memory for face-name associations.

Strategies for learning face-name associations are generally difficult and time-consuming. However, research has shown that saying a word aloud improves our memory for that word relative to words from the same set that were read silently. Such production effects have been shown for words, pictures, text material, and even word pairs. Can production improve memory for face-name associations? In Experiment 1, participants studied face-name pairs by reading half of the names aloud and half of the names silently, and were tested with cued recall. In Experiment 2, names were repeated aloud (or silently) for the full trial duration. Neither experiment showed a production effect in cued recall. Bayesian analyses showed positive support for the null effect. One possibility is that participants spontaneously implemented more elaborate encoding strategies that overrode any influence of production. However, a more likely explanation for the null production effect is that only half of each stimulus pair was produced-the name, but not the face. Consistent with this explanation, in Experiment 3 a production effect was not observed in cued recall of word-word pairs in which only the target words were read aloud or silently. Averaged across all 3 experiments, aloud targets were more likely to be recalled than silent targets (though not associated with the correct cue). The production effect in associative memory appears to require both members of a pair to be produced. Surprisingly, production shows little promise as a strategy for improving memory for the names of people we have just met. (PsycINFO Database Record

New Soft-Encoding Relay (SoER) Mechanisms for Wireless Relay Systems: Convolutional and Turbo Constructions

A two-hop parallel-relay network is considered in this paper. Conventional schemes investigating the coding strategies at the relay(s) have largely focused on hard encoding, with the exception of one pioneering strategy that proposed a soft distributed encoding using the soft estimate (tanh-based) information. To fully harness the gain promised by soft encoding, this paper focuses on distributed soft encoding strategies at the relays. Unlike the previous work that favors the tanh form for soft encoding, we advocate the range-limited log-likelihood ratios (rLLR) as a better way for the relays to capture the reliability of the messages sent by the sender, and especially to further soft-encode these messages. Based on this, we develop a simple but effective soft-encoding relay (SoER) strategy that exploits the useful features of rLLR. Specifically, the close resemblance of rLLR to the tanh form allows us to derive a very simple convolutional encoding, and the piece-wise linearity of rLLR allows us to evaluate the codeword probability density function (PDF) analytically, which further allows us to derive a Viterbi decoding algorithm using a more precise PDF (in addition to the Gaussian-approximated Viterbi algorithm). We finally extend the nonrecursive convolutional SoER strategy to the turbo SoER strategy. Simulation results confirm the efficiency of the new proposed SoER schemes.

Does the Way we Memorize Information Depend on the Way We are Going to Use It?

Existing research has shown modality-specific differences in short-term memory performance. Almost all previous studies have manipulated the input information without considering the way it will be used at output. In the current study, participants memorized spatially ordered arrays of letter-like shapes simultaneously shown on a screen, and recalled the stimuli by (i) drawing them on a sheet of paper, (ii) typing them on a keyboard according to a specified item-to-key map, and (iii) pronouncing them aloud using an item-to-letter map suggested by the letter-like items’ appearance. It was assumed that manipulating the output modality using the fixed stimuli set would lead to favoring different encoding strategies and subsequently result in different error patterns. Although visual input seems to be the main determinant of overall error rates in the drawing, typing and pronouncing tasks, less prominent but robust output-related differences between these tasks were also found. The pen and paper copying task showed a significant excess of substitutions called “upside down errors” and incorrect order responses. The typing task showed a significant excess of omissions. The pronouncing task showed a significant excess of mirror errors and the lowest rate of 90-degree rotations. The differences among patterns of errors in the different tasks are consistent with the hypothesized impact of the output modality on the way that visual information is stored in working memory.

The Effect of Encoding strategy and Transfer Appropriate Processing on Prospective Memory Performance

The Effect of Encoding strategy and Transfer Appropriate Processing on Prospective Memory Performance

What-where-when memory and encoding strategies in healthy aging.

Older adults exhibit disproportionate impairments in memory for item-associations. These impairments may stem from an inability to self-initiate deep encoding strategies. The present study investigates this using the “treasure-hunt task”; a what–where–when style episodic memory test that requires individuals to “hide” items around complex scenes. This task separately assesses memory for item, location, and temporal order, as well as bound what–where–when information. The results suggest that older adults are able to ameliorate integration memory deficits by using self-initiated encoding strategies when these are externally located and therefore place reduced demands on working memory and attentional resources.

Improving encoding strategies as a function of test knowledge and experience.

Information that is produced or generated during learning is better remembered than information that is passively read, a phenomenon known as the generation effect. Prior research by deWinstanley and Bjork (Memory & Cognition, 32, 945-955, 2004) has shown that learners, after experiencing the memorial benefits of generation in the context of a fill-in-the-blank test following the study of a text passage containing both to-be-read and to-be-generated items, become more effective encoders of to-be-read items on a second passage, thus eliminating the generation effect on a subsequent memory test. Current explanations of this phenomenon assume that learners need to actually experience the generation advantage on the test of the first passage to become more effective encoders of to-be-read items on the second passage. The results of the present research, however, suggest otherwise. Although experiencing a test of the first passage does appear to be critical for leading participants to become better encoders on the second passage, experiencing a generation advantage on the test for the first passage is not. More generally, these results shine new light on the generation effect as well as how and why taking tests has the potential to improve subsequent learning.

The role of encoding strategy in younger and older adult associative recognition: A think-aloud analysis.

Older adults have especially poor recognition memory for word pairs, and research suggests this associative deficit manifests primarily in older adults' higher rates of false alarms. This could result from older adults either failing to generate meaningful (deep) mediators at study, or failing to benefit from having generated deep mediators at test. Younger and older adults performed a recognition memory task for words and word pairs. A think-aloud analysis of their spontaneous encoding strategies (repetition, shallow mediators, deep mediators) revealed that generation of deep mediators did not differ between younger and older adults, and was associated with high hit rates for items and associates in both age groups. However, generation of deep mediators was inversely related to false alarm rates in younger adults but not older adults. A trial-level analysis of encoding strategies and recognition responses revealed that younger adults benefited from having generated deep mediators when presented with corresponding recombined pairs at test as shown in their lower false alarm rates. In contrast, older adults who generated deep mediators during study (e.g., to blanket-figure) did not benefit from having done so when they encountered the corresponding recombined pairs at test (blanket-summer and district-figure). Their false alarm rates to pairs at test were unrelated to generation of deep mediators at study. These results suggest that many older adults have difficulty retrieving their mediators when presented with recombined pairs at test, or their mediators are not distinct enough to distinguish intact pairs from recombined pairs at test, or some combination of both. (PsycINFO Database Record

Jointly Optimized Reed-Muller Codes for Multi-Level Multi-Relay Coded-Cooperative VANETS

In this paper, we present the well-known Reed–Muller (RM) codes for multilevel multirelay vehicular adhoc networks, which can enjoy coded-cooperation among network nodes. At first, we present the code construction principles for a single node/relay scenario and then extend the design principles to the two-level two-relay and, finally, to multilevel multirelay scenarios. The term “level” refers to the fact that different order RM code is used at each relaying node. Plotkin's construction is exploited to utilize RM codes in such coded-cooperative schemes. To achieve an optimum code at the destination node, proper encoding strategy needs to be employed at the relay node. Therefore, we propose a design criteria and an efficient algorithm for proper bit selection at the relay nodes to achieve the best possible code at the destination. It is observed that the increase in the number of levels as well as relays result in better channel code at the destination, as compared to the lesser number of relays, however, at the cost of increased decoding complexity. The channels considered to analyze the bit error rate (BER) performances of proposed coded-cooperative schemes are fast and slow Rayleigh fading channels. At the destination, soft decision maximum likelihood decoding is employed. Numerical simulations show that the single-relay RM coded-cooperative scheme provides significant BER performance gains over the noncooperative and state-of-the-art distributed turbo coded-cooperative schemes under identical conditions.

You can go your own way: effectiveness of participant-driven versus experimenter-driven processing strategies in memory training and transfer

ABSTRACTCognitive training programs that instruct specific strategies frequently show limited transfer. Open-ended approaches can achieve greater transfer, but may fail to benefit many older adults due to age deficits in self-initiated processing. We examined whether a compromise that encourages effort at encoding without an experimenter-prescribed strategy might yield better results. Older adults completed memory training under conditions that either (1) mandated a specific strategy to increase deep, associative encoding, (2) attempted to suppress such encoding by mandating rote rehearsal, or (3) encouraged time and effort toward encoding but allowed for strategy choice. The experimenter-enforced associative encoding strategy succeeded in creating integrated representations of studied items, but training-task progress was related to pre-existing ability. Independent of condition assignment, self-reported deep encoding was associated with positive training and transfer effects, suggesting that the most beneficial outcomes occur when environmental support guiding effort is provided but participants generate their own strategies.

The rise and fall of hybrid visual and memory search

In hybrid search, observers search through arrays of visually presented items for any of a set of targets held in memory; think of looking on a store shelf for items on your grocery list, searching luggage x-rays for potential banned items, or chest x-rays for signs of cancer. As the size of the memory sets used in hybrid search increased, descriptions of the RT by set size function moved from linear (Shiffrin & Schneider, 1977) to logarithmic (Wolfe, 2012). In order to study hybrid search at larger set sizes, with greater resolution, and as a function of expertise, I utilized the Airport Scanner (Kedlin Co., www.airportscannergame.com) dataset (see Mitroff and Biggs 2014). Airport Scanner is a game for mobile devices, which simulates searching through baggage x-rays for threats under time constraints. Players move through five ranks as they acquire game expertise, from Trainee to Elite. Critically, new items are added to the list of potential threats as the game progresses. Eliminating trainees to reduce potential learning effects, I analyzed only trials (bags) with a single target. This left 3,491,664 trials from 18,595 players. Memory set size(potential threats) ranged from 3 to 155 items. Visual set size had no influence on performance. For set sizes from 6-12, the logarithmic relationship held. However, across the full range of set sizes, at all expertise levels, reaction time was best described as a quadratic, rather than logarithmic, function of set size. For the low expertise groups, the curve opened upward, while at high expertise, it opened downward. These data suggest that encoding and retrieval strategies in hybrid search change in a complex fashion as the size of the memory set increases, and as observers gain more expertise with the task. Models developed for small set sizes may not generalize to realistically large set sizes. Meeting abstract presented at VSS 2015. Language: en

Hyperpolarized (129) Xe imaging of the rat lung using spiral IDEAL.

To implement and optimize a single-shot spiral encoding strategy for rapid 2D IDEAL projection imaging of hyperpolarized (Hp) (129) Xe in the gas phase, and in the pulmonary tissue (PT) and red blood cells (RBCs) compartments of the rat lung, respectively. A theoretical and experimental point spread function analysis was used to optimize the spiral k-space read-out time in a phantom. Hp (129) Xe IDEAL images from five healthy rats were used to: (i) optimize flip angles by a Bloch equation analysis using measured kinetics of gas exchange and (ii) investigate the feasibility of the approach to characterize the exchange of Hp (129) Xe. A read-out time equal to approximately 1.8 × T2* was found to provide the best trade-off between spatial resolution and signal-to-noise ratio (SNR). Spiral IDEAL approaches that use the entire dissolved phase magnetization should give an SNR improvement of a factor of approximately three compared with Cartesian approaches with similar spatial resolution. The IDEAL strategy allowed imaging of gas, PT, and RBC compartments with sufficient SNR and temporal resolution to permit regional gas exchange measurements in healthy rats. Single-shot spiral IDEAL imaging of gas, PT and RBC compartments and gas exchange is feasible in rat lung using Hp (129) Xe. Magn Reson Med 76:566-576, 2016. © 2015 Wiley Periodicals, Inc.

Differences in prefrontal cortex activation and deactivation during strategic episodic verbal memory encoding in mild cognitive impairment.

In this study we examined differences in fMRI activation and deactivation patterns during episodic verbal memory encoding between individuals with MCI (n = 18) and healthy controls (HCs) (n = 17). Participants were scanned in two different sessions during the application of self-initiated or directed instructions to apply semantic strategies at encoding of word lists. MCI participants showed reduced free recall scores when using self-initiated encoding strategies that were increased to baseline controls' level after directed instructions were provided. During directed strategic encoding, greater recruitment of frontoparietal regions was observed in both MCI and control groups; group differences between sessions were observed in the ventromedial prefrontal cortex and the right superior frontal gyrus. This study provides evidence suggesting that differences of activity in these regions may be related to encoding deficits in MCI, possibly mediating executive functions during task performance.

Plane-wave least-squares reverse time migration for rugged topography

We present a method based on least-squares reverse time migration with plane-wave encoding (P-LSRTM) for rugged topography. Instead of modifying the wave field before migration, we modify the plane-wave encoding function and fill constant velocity to the area above rugged topography in the model so that P-LSRTM can be directly performed from rugged surface in the way same to shot domain reverse time migration. In order to improve efficiency and reduce I/O (input/output) cost, the dynamic encoding strategy and hybrid encoding strategy are implemented. Numerical test on SEG rugged topography model show that P-LSRTM can suppress migration artifacts in the migration image, and compensate amplitude in the middle-deep part efficiently. Without data correction, P-LSRTM can produce a satisfying image of near-surface if we could get an accurate near-surface velocity model. Moreover, the pre-stack PLSRTM is more robust than conventional RTM in the presence of migration velocity errors.