Noise Letters Research Articles

Binocular and Monocular Resolution Thresholds throughout Adulthood for Luminance-Modulated and Contrast-Modulated Noise Letters

Contrast-modulated (CM) noise stimuli are thought to be processed in higher, more binocular visual areas compared to luminance-modulated (LM) stimuli, and the ability to perceive them may be more susceptible to ageing. The aim of this study was to determine monocular and binocular resolution thresholds for LM and CM noise letters throughout adulthood. Resolution thresholds for LM and CM noise letters were measured in 25 participants (age 21-70 years old) under monocular and binocular viewing. Stimuli were H, O, T and V letters created by adding or multiplying a luminance modulation function to a binary white noise carrier to create LM and CM noise letters, respectively. Resolution thresholds, determined using a 2-down-1-up staircase procedure, were lower for LM, than for CM, stimuli in both monocular and binocular viewing conditions (p<0.05). Binocular summation ratio for CM noise letters was significantly higher than that for LM noise letters (p<0.05) but declined rapidly with increasing age. For the youngest age group (20-29 years old), binocular resolution threshold was 39% better (~1.5-line improvement on the clinical letter chart) than monocular resolution threshold for CM noise letters, but only 15% better (~0.5-line improvement) when measured with LM noise letters. Binocular performance for CM noise letters declines at a faster rate with increasing age compared to that for LM noise letters. Visual function measurement with contrast-modulated stimuli might be useful to detect subtle binocular vision anomalies that may occur in early adulthood, which may be missed if measured with luminance-based stimuli alone.

Unsolved Problems of Noise Preface to the UPoN-2018 Special Issue of Fluctuation and Noise Letters

Unsolved Problems of Noise Preface to the UPoN-2018 Special Issue of Fluctuation and Noise Letters

Conflict adaptation and interference suppression in stroke-induced aphasia: Evidence from multiple-single case studies

Conflict adaptation and interference suppression in stroke-induced aphasia: Evidence from multiple-single case studies

Visual acuity measured with luminance-modulated and contrast-modulated noise letter stimuli in young adults and adults above 50 years old

The human visual system is sensitive in detecting objects that have different luminance level from their background, known as first-order or luminance-modulated (LM) stimuli. We are also able to detect objects that have the same mean luminance as their background, only differing in contrast (or other attributes). Such objects are known as second-order or contrast-modulated (CM), stimuli. CM stimuli are thought to be processed in higher visual areas compared to LM stimuli, and may be more susceptible to ageing. We compared visual acuities (VA) of five healthy older adults (54.0±1.83 years old) and five healthy younger adults (25.4±1.29 years old) with LM and CM letters under monocular and binocular viewing. For monocular viewing, age had no effect on VA [F(1, 8)= 2.50, p> 0.05]. However, there was a significant main effect of age on VA under binocular viewing [F(1, 8)= 5.67, p< 0.05]. Binocular VA with CM letters in younger adults was approximately two lines better than that in older adults. For LM, binocular summation ratios were similar for older (1.16±0.21) and younger (1.15±0.06) adults. For CM, younger adults had higher binocular summation ratio (1.39±0.08) compared to older adults (1.12±0.09). Binocular viewing improved VA with LM letters for both groups similarly. However, in older adults, binocular viewing did not improve VA with CM letters as much as in younger adults. This could reflect a decline of higher visual areas due to ageing process, most likely higher than V1, which may be missed if measured with luminance-based stimuli alone.

Visual acuity measured with luminance-modulated and contrast-modulated noise letter stimuli in young adults and adults above 50 years old.

The human visual system is sensitive in detecting objects that have different luminance level from their background, known as first-order or luminance-modulated (LM) stimuli. We are also able to detect objects that have the same mean luminance as their background, only differing in contrast (or other attributes). Such objects are known as second-order or contrast-modulated (CM), stimuli. CM stimuli are thought to be processed in higher visual areas compared to LM stimuli, and may be more susceptible to ageing. We compared visual acuities (VA) of five healthy older adults (54.0±1.83 years old) and five healthy younger adults (25.4±1.29 years old) with LM and CM letters under monocular and binocular viewing. For monocular viewing, age had no effect on VA [F(1, 8)= 2.50, p> 0.05]. However, there was a significant main effect of age on VA under binocular viewing [F(1, 8)= 5.67, p< 0.05]. Binocular VA with CM letters in younger adults was approximately two lines better than that in older adults. For LM, binocular summation ratios were similar for older (1.16±0.21) and younger (1.15±0.06) adults. For CM, younger adults had higher binocular summation ratio (1.39±0.08) compared to older adults (1.12±0.09). Binocular viewing improved VA with LM letters for both groups similarly. However, in older adults, binocular viewing did not improve VA with CM letters as much as in younger adults. This could reflect a decline of higher visual areas due to ageing process, most likely higher than V1, which may be missed if measured with luminance-based stimuli alone.

A COMBINATION FORECAST FOR ENERGY-RELATEDCO2EMISSIONS IN THE UNITED STATES

This paper seeks to provide an alternative forecast to that provided by the Energy Information Administration (EIA) on energy-related monthly CO2 emissions in the United States. The data on CO2 emissions from petroleum, natural gas, coal and total fossil fuels obtained via the EIA covering the period January 2005 to November 2013 is analysed and then forecasted using ARIMA, Holt-Winters, and Exponential Smoothing prior to introducing the Singular Spectrum Analysis (SSA) technique for CO2 emissions forecasting. A new combination forecast (EIA-SSA) is also introduced by merging the SSA and EIA forecasts, and is seen outperforming all models including the EIA forecast. Finally, the EIA-SSA model is used to provide an alternative 12 month ahead outlook for US energy-related CO2 emissions from December 2013 to November 2014. This research is expected to influence the methodology adopted by the EIA for forecasting CO2 emissions in the future by improving the accuracy of the forecasts, and the impact of this study will be clearer upon comparing the actual CO2 emissions in US with the EIA, and EIA-SSA forecasts over the 12 month period which follows.

Individual Differences in Subconscious Motor Control Predicted by GABA Concentration in SMA

Subliminal visual stimuli affect motor planning, but the size of such effects differs greatly between individuals. Here, we investigated whether such variation may be related to neurochemical differences between people. Cortical responsiveness is expected to be lower under the influence of more of the main inhibitory neurotransmitter, GABA. Thus, we hypothesized that, if an individual has more GABA in the supplementary motor area (SMA)--a region previously associated with automatic motor control--this would result in smaller subliminal effects. We measured the reversed masked prime--or negative compatibility--effect, and found that it correlated strongly with GABA concentration, measured with magnetic resonance spectroscopy. This occurred specifically in the SMA region, and not in other regions from which spectroscopy measurements were taken. We replicated these results in an independent cohort: more GABA in the SMA region is reliably associated with smaller effect size. These findings suggest that, across individuals, the responsiveness of subconscious motor mechanisms is related to GABA concentration in the SMA.

Analysis of Antarctic Ice Core Data (EPICA Dome C) with Flicker-Noise Spectroscopy

Evolution of Earth’s climate system over the past 800,000 years represents a complex process with successions of uneven glacial and interglacial periods. The length, amplitudes, and development of each climate cycle depend on a number of different factors, including the orbital parameters attributed to insolation and the complex responses of the Earth system to solar radiation primarily through the amplification by Earth’s albedo and greenhouse gas and secondarily through a system of heat reservoirs, such as ice sheet and deep ocean, distributed throughout our planet. The purpose of this study is to analyze the transitions related to climate cycles in Antarctic ice core data (EPICA Dome C) of deuterium composition and dust concentration recorded for the past 800,000 years [1] using Flicker-Noise Spectroscopy (FNS), an analytical toolset for the extraction and analysis of information in stochastic time and space series, containing both regular and chaotic components, by using power spectra and difference moments (structural functions) of various orders [2].The FNS nonstationarity factors for the deuterium composition and dust (logarithm) concentration, which represent the normalized discrete derivative of the second-order structural function of the source signal with respect to a given shifted “window” interval, were built for different intervals of averaging to identify the major changes in the dynamics of both time series and their precursors. It is shown that when displayed together with the source signals, the positive peaks in the nonstationarity factors provide more reliable estimates of the transition of the climate system from one sub-period to another within a specific climate cycle as compared to predefined thresholds in dust or deuterium values. For climatic transitions, the power spectral estimates of the nonstationarity factors contain several periodicities in addition to the orbital ones. These frequencies may be attributed to specific heat accumulation and discharge processes in the climate system. The results of this study demonstrate the potential of FNS in the analysis of climate data series and may be used in refining climate transition models.This study was supported by the Russian Foundation for Basic Research, project no. 08-02-00230a.[1] Lambert F., et al. (2008) Dust-climate couplings over the past 800,000 years from the EPICA Dome C ice core, Nature 452, 616-619.[2] Timashev, S. F., Polyakov Yu. S. (2007) Review of flicker noise spectroscopy in electrochemistry, Fluctuations and Noise Letters 7(2), R15-R47.

Analysis of Antarctic Ice Core Data (EPICA Dome C) with Flicker-Noise Spectroscopy

AbstractEvolution of Earth’s climate system over the past 800,000 years represents a complex process with successions of uneven glacial and interglacial periods. The length, amplitudes, and development of each climate cycle depend on a number of different factors, including the orbital parameters attributed to insolation and the complex responses of the Earth system to solar radiation primarily through the amplification by Earth’s albedo and greenhouse gas and secondarily through a system of heat reservoirs, such as ice sheet and deep ocean, distributed throughout our planet. The purpose of this study is to analyze the transitions related to climate cycles in Antarctic ice core data (EPICA Dome C) of deuterium composition and dust concentration recorded for the past 800,000 years [1] using Flicker-Noise Spectroscopy (FNS), an analytical toolset for the extraction and analysis of information in stochastic time and space series, containing both regular and chaotic components, by using power spectra and difference moments (structural functions) of various orders [2].The FNS nonstationarity factors for the deuterium composition and dust (logarithm) concentration, which represent the normalized discrete derivative of the second-order structural function of the source signal with respect to a given shifted “window” interval, were built for different intervals of averaging to identify the major changes in the dynamics of both time series and their precursors. It is shown that when displayed together with the source signals, the positive peaks in the nonstationarity factors provide more reliable estimates of the transition of the climate system from one sub-period to another within a specific climate cycle as compared to predefined thresholds in dust or deuterium values. For climatic transitions, the power spectral estimates of the nonstationarity factors contain several periodicities in addition to the orbital ones. These frequencies may be attributed to specific heat accumulation and discharge processes in the climate system. The results of this study demonstrate the potential of FNS in the analysis of climate data series and may be used in refining climate transition models.This study was supported by the Russian Foundation for Basic Research, project no. 08-02-00230a.[1] Lambert F., et al. (2008) Dust-climate couplings over the past 800,000 years from the EPICA Dome C ice core, Nature 452, 616-619.[2] Timashev, S. F., Polyakov Yu. S. (2007) Review of flicker noise spectroscopy in electrochemistry, Fluctuations and Noise Letters 7(2), R15-R47.

Using the Attention Network Test to predict driving test scores

Driving is a complex multi-factorial task that taps underlying mechanisms of cognition and attention. Not surprisingly, therefore, many tests of cognition and attention are significantly associated with driving outcomes. In this article, we introduce driving researchers and clinicians with an interest in driving to the Attention Network Test (ANT), which to our knowledge has not previously been used in driving research. It is a recently developed test that is based on a neural network model of the human attention system. It combines elements of Posner’s cuing paradigm [Posner, M.I., 1980. Orienting of attention. Quarterly Journal of Experimental Psychology 32, 3–25.] with the Eriksen & Eriksen flanker task [Eriksen, B.A., Eriksen, C.W., 1974. Effects of noise letters upon the identification of a target letter in a nonsearch task. Perception & Psychophysics 16, 143–149.], and provides measures of three distinct functions of attention: alerting, orienting, and executive function. Our results demonstrate that the ANT has very good concurrent validity with the Useful Field of View (UFOV), and that it is comparable to UFOV in its ability to predict road test scores for a simulated drive. These findings suggest that further investigation of the usefulness of the ANT as a tool for driving researchers and clinicians is merited.

Obsessive–compulsive tendencies are associated with a focused information processing strategy

The study examined the hypothesis that obsessive–compulsive (OC) tendencies are related to a reliance on focused and serial rather than a parallel, speed-oriented information processing style. Ten students with high OC tendencies and 10 students with low OC tendencies performed the flanker task, in which they were required to quickly classify a briefly presented target letter (S or H) that was flanked by compatible (e.g., SSSSS) or incompatible (e.g., HHSHH) noise letters. Participants received 4 blocks of 100 trials each, two with 50% compatible trials and two with 80% compatible trials and were informed of the probability of compatible trials before the beginning of each block. As predicted, high OC participants, as compared to low OC participants, had slower overall reaction time (RT) and lower tendency for parallel processing (defined as incompatible trials RT minus compatible trials RT). Low, more than high OC participants tended to adjust their focused/parallel processing including a shift towards parallel processing in blocks with 80% compatible trials and in trials following compatible trials. Implications of these results to the cognitive theory and therapy of OCD are discussed.

Enhanced coding for exponentially distributed signals using suprathreshold stochastic resonance

Our previous work on stochastic resonance (SR) in threshold based systems proved that the SR effect is dependent on the nature of the input signal distribution; more specifically, for certain types of signal distribution SR is not observed [Das A, Stocks NG, Nikitin A, Hines EL. Quantifying stochastic resonance in a single threshold detector for random aperiodic signals. Fluctuation Noise Lett 2004;4:L247–65]. Here we show that suprathreshold stochastic resonance (SSR) – a novel and distinct form of SR – removes this limitation and hence leads to the conclusion that SSR can probably enhance the transmission of signals of any distribution and amplitude. SSR effects are studied in a parallel array of identical nonlinear threshold based devices. A double exponential signal distribution is chosen because this distribution did not demonstrate conventional SR effects in a single threshold device [Das A, Stocks NG, Nikitin A., Hines EL. Quantifying Stochastic resonance in a single threshold detector for random aperiodic signals. Fluctuation and Noise Letters 2004;4:L247-L265.]. SSR as a possible mechanism for enhancing transmission of speech signals in the human ear is also discussed.

Inefficient response inhibition in individuals with mild cognitive impairment

Individuals diagnosed with mild cognitive impairment (MCI) show primary deficits in memory and are at increased risk for developing Alzheimer's disease (AD). In light of recent evidence that executive cognitive deficits are common in AD and may be detectable in individuals diagnosed with MCI, we extend these findings to the investigation of response inhibition, an essential aspect of executive cognitive control. Twenty MCI patients and 20 healthy controls (HC) completed an arrow version of the flanker task [Eriksen, B. A., & Eriksen, C. W. (1974). Effects of noise letters upon the identification of target letters in a non-search task. Perception & Psychophysics, 16, 143–149] in which participants responded to a target arrow surrounded by distractors (i.e., flankers) that signaled a same (congruent) or a conflicting (incongruent) response. Reaction time (RT) increased in both groups when flankers signaled an incongruent response, but more so among MCI patients. MCI patients taking a cholinesterase inhibitor showed smaller flanker interference effects than those not taking this medication. Analysis of the flanker effect as a function of the entire RT distribution indicated that MCI patients show increasing interference at the slowest segments of the distribution, a finding that implicates deficient inhibition of the incongruent response [Ridderinkhof, K. R. (2002). Activation and suppression in conflict tasks: Empirical clarification through distributional analyses. In W. Prinz & B. Hommel (Eds.), Common mechanisms in perception and action. Attention & performance, Vol. XIX (pp. 494–519). Oxford: Oxford University Press]. These results suggest that deficits in response inhibition are detectable in MCI patients and merit further investigation as to whether these changes aid prediction of which MCI patients convert to AD.

Motivated executive attention—incentives and the noise-compatibility effect

The motivational context is an important variable in experimental research. The present study investigates the effects of reward and punishment on performance in a noise-compatibility-task [Eriksen, B.A., Eriksen, C.W., 1974. Effects of noise letters upon the identification of a target letter in a nonsearch task. Perception and Psychophysics 16 (1), 143–149]. Flanking distractors indicated a response, which was identical, undefined, or opposite to the appropriate response indicated by the central target. At the beginning of each trial a cue specified positive, negative or no reinforcement in order to elicit three different motivational states: approach, avoidance and a non-reinforced neutral state. Fifty-three subjects (aged 20–27 years) participated. Incompatibility effects on reaction times and percentage errors were analysed as a function of motivational state, as were the effects on two ERPs, the lateralised readines potential (LRP) and the N2. Error and LRP data showed effects of reinforcement only when incompatible distractors were present, which indicates that controlled processing depends on the motivational context. In contrast to previous findings, the N2 was not found to depend on response conflict.

A psychophysiological study on the function of the response-stop in the Eriksen task1,2

: In the Eriksen task, we examined the hypothesis (Iwaki, 1998) that a negative event-related potential, which was enlarged at the frontal site synchronized with the presentation of an erroneous response causing stimulus, is related to the response-stop function. Fourteen subjects responded selectively with their hands to the stimuli that consisted of a central target letter and surrounding compatible noise letters (e.g., HHHHH) or incompatible noise (e.g., SHHHS for small-conflict condition or SSHSS for large-conflict). The results showed that the increased negativity for the incompatible stimuli was synchronized with the stimulus onset but not with the response. Based on the hypothesis above, it is predicted that greater enhancement of an erroneous response by a stimulus causes the response-stop to work harder in order to avoid an error, and this results in the larger negativity. This was supported by the evidence showing that the negativity was largest for the large-conflict incompatible stimulus, followed by the small-conflict, and then the compatible. We also discuss the possibility that the negativity is the NO-GO potential concerned with the response-stop function.

Neural activation during response competition.

The flanker task, introduced by Eriksen and Eriksen [Eriksen, B. A., & Eriksen, C. W. (1974). Effects of noise letters upon the identification of a target letter in a nonsearch task. Perception & Psychophysics, 16, 143--149], provides a means to selectively manipulate the presence or absence of response competition while keeping other task demands constant. We measured brain activity using functional magnetic resonance imaging (fMRI) during performance of the flanker task. In accordance with previous behavioral studies, trials in which the flanking stimuli indicated a different response than the central stimulus were performed significantly more slowly than trials in which all the stimuli indicated the same response. This reaction time effect was accompanied by increases in activity in four regions: the right ventrolateral prefrontal cortex, the supplementary motor area, the left superior parietal lobe, and the left anterior parietal cortex. The increases were not due to changes in stimulus complexity or the need to overcome previously learned associations between stimuli and responses. Correspondences between this study and other experiments manipulating response interference suggest that the frontal foci may be related to response inhibition processes whereas the posterior foci may be related to the activation of representations of the inappropriate responses.

A study on the response selection and inhibition in a cognitive conflict task using event-related potentials

This study examined the hypothesis (Eriksen & Schultz, 1979) that a subject checks whether a prepared response is correct or not in the Eriksen and Eriksen (1974) cognitive conflict task, using event-related potentials (ERPs). Fourteen right-handed subjects were required to respond selectively to a central target letter flanked with compatible (e.g., HHHHHHH) or incompatible (e.g., SSSHSSS) noise letters, or not to respond to asterisks (*******). The results showed that the lateralized readiness potential indicating an incorrect preparation and the NO-GO potential reflecting a response inhibition emerged for incompatible stimuli. These findings indicate that a prepared response was recognized as erroneous, and was inhibited. Therefore, it is suggested that the check operation functioned in the cognitive conflict task. Furthermore, the result that the NO-GO potential latency for incompatible stimuli was longer than that for NO-GO stimuli suggests that the timing of NO-GO decision and response inhibition by the check operation influenced the NO-GO potential latency.

A study of information processing of cognitive conflict using event-related potentials

This study examined whether cognitive conflict, reported by Eriksen and Eriksen (1974), could be explained by a model of reciprocal inhibition between correct and incorrect response preparation. Subjects responded selectively to a central target letter with flanking compatible (e.g., HHHHH) or incompatible (e.g., SSHSS) noise letters. In the mixed condition all four stimuli were mixed randomly in a block, and in the blocked condition only two stimuli with identical noises were used. The results showed that the reaction times to incompatible stimuli were delayed in the mixed condition compared with that to compatible stimuli, while the delay was significantly reduced in the blocked condition. This blocking effect was also shown on P3 latencies, an event-related potential measure of stimulus evaluation, but not on lateralized readiness potentials (LRPs), a measure of response preparation. Furthermore, irrespective of blocked/mixed conditions, LRPs indicating incorrect preparation were observed. These findings suggest that cognitive conflict could not be explained by the reciprocal inhibition model based on response preparation, but by a model based on stimulus evaluation.

Adult age differences in attention: filtering or selection?

We examined the effect of target letter redundancy for target-only (TO) and target-plus-noise (TPN) trials on a visual search, divided attention task where target letters were presented in one or two corners of a two-corner display. Half of the two-letter displays also included a noise letter. In both Experiment 1 (two-choice vs go/no-go) and Experiment 2 (all go/no-go), older adults showed larger redundancy gains than did young adults, and this effect did not interact with task type or visual similarity. However, for the "no-go" trials in both experiments, there were no age differences in overall errors. These results suggest that there are age differences in the activation of selective attention rather than age differences in inhibitory control. In Experiment 2, young adults under lower-luminance presentation conditions (18 cd/m2) showed a smaller redundancy gain than did older adults under higher-luminance presentation conditions (40 cd/m2). These results provided further support of the age differences in activation interpretation, as well as indicating that older adults' larger redundancy gain was not due to an age decrement in retinal illuminance.

Influence of Response Selection and Noise Similarity on Age Differences in the Redundancy Gain

We examined the impact of target redundancy for target-plus-noise (TPN) and target-only (TO) trials. Experiment 1 manipulated response selection load (two-choice vs go/no-go) and Experiment 2 (all two-choice) varied noise redundancy (single or cumulative noise letters) on a visual search, divided attention task in which target letters were presented in one, two, or three corners of a four-corner display. Half of the trials also included noise letters. For Experiment 1, there was a definite redundancy gain for TO trials. Furthermore, older adults, relative to young adults, evidenced an even larger redundancy gain for TO trials than for TPN trials, although response selection load did not interact with age. These results are consistent with the notion that older adults exhibit a processing resources decrement. For Experiment 2, older adults evidenced a relatively larger redundancy gain for TPN trials than for TO trials, and this was especially the case for TPN trials in which all nontarget locations were filled with noise letters. Experiment 2 results are consistent with the notion that older adults also exhibit a selective attention decrement.