Journal Papee
Structural identifiability of Order-of-Processing models: When do different cognitive architectures generate identical response time distributions
*Khodami, A.
Journal of Mathematical Psychology
Abstract: The Order-of-Processing (OP) method, introduced by Goldstein and Fisher in 1991, provides a powerful framework for deriving response-time distributions from stochastic network models of cognitive architecture. While the forward problem—predicting response-time distributions from a hypothesised network structure and process parameters—is well understood, the inverse problem remains unexamined: given an observed response-time distribution, when can researchers uniquely recover the underlying rate parameters, and when can they not? This work studies a restricted path-based subclass of OP models and develops a theory of structural identifiability for that subclass using moment-generating functions, Laplace-transform arguments, and diagram symmetries. The work shows that, under stated regularity and no-cancellation conditions, the multiset of rate parameters is generically recoverable from the reduced rational transform, whereas assignment of those rates to specific process labels can fail whenever the OP diagram contains nontrivial permutation symmetries. The work formalises the symmetry group of an OP diagram, show how its action induces observationally equivalent parameter assignments, and distinguish this within-framework non-identifiability from the broader serial–parallel mimicry problem. Applications to visual-search architectures illustrate symmetric, asymmetric, and partially symmetric cases and clarify the inferential scope of OPM-based analyses. The results provide practical guidance on when additional constraints or experimentally induced asymmetries are needed before fitted OPM parameters can be interpreted psychologically.
Journal Paper / Brief Communication
Temporal perceptual training enhances visual acuity in adult amblyopia: a single-case study
Khodami, A.*, Battaglini L.
Nature Eye
Abstract:
Journal Paper
Stress effects on cognition: Evidence for stress-related disruption of attention and inhibitory control
Khodami, A.*, Contemori G., Battaglini L., Jansarvatan M.
Heliyon
Abstract: While stress can impair cognitive functions, including attention and inhibition, it is not always deleterious; e.g., stress could also increase alertness, motivation, and concentration. Limited research has examined these effects in clinical populations experiencing high perceived stress. The current study investigated the impact of perceived stress levels, as measured by the Perceived Stress Scale (PSS), on attention and inhibition in 91 participants grouped into high, moderate, and low perceived stress levels. Participants completed online versions of the Stroop and Go/No-Go tasks to assess attention and inhibition. Results revealed that participants with higher perceived stress exhibited longer reaction times and fewer correct responses than those reporting lower stress across both tasks. ANOVA revealed significantly poorer performance on the Stroop and Go/No Go tasks among individuals in the high-stress group compared with the moderate- and low-stress groups. Introducing auditory or visual interference further disrupted cognitive performance in the high-stress group. These findings indicate that raised perceived stress negatively impacts attention and inhibition. The study provides evidence that chronic stress may impede cognitive abilities and suggests that further research should examine stress effects in clinical cohorts. This investigation makes a meaningful contribution by demonstrating the deleterious impacts of high perceived stress on cognition in a clinical sample, addressing a gap in the literature.
Journal Paper
A Simulated Visual Field Defect Impairs Temporal Processing: An Effect Not Modulated by Emotional Faces
Khodami, A.*, Battaglini L.,
Vision, 2025
Abstract: Temporal processing is fundamental to visual perception, yet little is known about how it functions under compromised visual field conditions or whether emotional stimuli, as reported in the literature, can modulate it. This study investigated temporal resolution using a two-flash fusion paradigm with a static, semi-transparent overlay that degraded the right visual hemifield of opacity 0.60 and examined the potential modulatory effects of emotional faces. In Experiment 1, participants were asked to report if they perceived one or two flashes presented at either −6° (normal vision) or +6° (beneath a scotoma) across eight interstimulus intervals, ranging from 10 to 80 ms with a step size of 10 ms. Results showed significantly impaired temporal discrimination in the degraded vision condition, with elevated thresholds 52.29 ms vs. 34.78 ms and reduced accuracy, particularly at intermediate ISIs 30–60 ms. In Experiment 2, we introduced emotional faces before flash presentation to determine whether emotional content would differentially affect temporal processing. Our findings indicate that neither normal nor scotoma-impaired temporal processing was modulated by the specific emotional content (angry, happy, or neutral) of the facial primes.
Preprint
Adaptive Reconstruction of Pupil Dynamics During Blink Data Loss: A Physiologically-Informed Exponential Recovery and Noise Modelling Framework
Khodami, A., Hosseini SM., Kireeva S.,
BioRxiv, 2025
Abstract: This paper presents a novel, physiologically inspired framework for reconstructing missing pupil data during blink-induced interruptions. Pupillometry has become integral to studies of cognition, emotion, and neural function, yet the frequent data gaps caused by blinks can compromise the accuracy of inferences drawn from pupil measurements. This approach addresses these challenges by introducing an exponential recovery model that dynamically adjusts its time constant in proportion to blink duration, thus capturing the non-linear dynamics of pupil responses more effectively than traditional interpolation methods. A localised noise estimation procedure further enhances realism by incorporating both signal-dependent and baseline noise derived from statistical properties of the data surrounding each blink. Additionally, a Savitzky–Golay filter is selectively applied to the reconstructed intervals, preserving key physiological features while mitigating high-frequency artefacts. To facilitate the implementation of our framework, we introduce PRPIP, a Python package that implements our methodology. This work demonstrates the effectiveness of this method using empirical pupil data from visual tasks, illustrating that the reconstructed signals maintain physiological fidelity across a range of blink durations. These findings underscore the potential of combining physiological principles with data-driven noise modelling to generate robust, continuous pupil traces. By offering a more accurate reconstruction of pupil size, this framework stands to advance pupillometric research in fields ranging from cognitive psychology to clinical neuroscience.
Preprint (Under Review)
A Dynamic Threshold-Based Method for Robust and Accurate Blink Detection in Eye-Tracking Data
Khodami, A.
BioRxiv, 2025
Abstract: Blink detection is a critical component of eye-tracking research, particularly in pupillometry, where data loss due to blinks can obscure meaningful insights. Existing methods often rely on fixed thresholds or device-specific noise profiles, which may lead to inaccuracies in detecting blink onsets and offsets, especially in heterogeneous datasets. This study introduces a novel blink detection model that dynamically adapts to varying pupil size distributions, ensuring robustness across different experimental conditions. The proposed method integrates dynamic thresholding, which adjusts based on the mean pupil size of valid samples, Gaussian smoothing, which reduces noise while preserving signal integrity, and adaptive boundary refinement, which refines blink onsets and offsets based on a trends in the smoothed data. Unlike traditional approaches that merge closely spaced blinks, this model treats each blink as an independent event, preserving temporal resolution, which is essential for cognitive and perceptual studies. The model is computationally efficient and adaptable to a wide range of sampling rates, from low-frequency (e.g., 250 Hz) to high-frequency (e.g., 2000 Hz) data, ensuring consistent blink detection across different eye-tracking setups, making it suitable for both real-time and offline eye-tracking applications. Experimental evaluations demonstrate its ability to accurately detect blinks across diverse datasets. By offering a more reliable and generalizable solution, this model advances blink detection methodologies and enhances the quality of eye-tracking data analysis across research domains.
Journal Paper
Combined transcranial alternating current stimulation and perceptual learning for vision improvement in a single-case study of cone dystrophy
Oletto CM, Khodami, A., et al.,
Brain Stimulation: Basic, Translational, and Clinical Research in Neuromodulation, 2025
Abstract: Cone dystrophy is a rare genetic disorder characterized by the progressive degeneration of cone photoreceptors, resulting in significant visual impairment. This multiple baseline single-case study explored the effects of combining peri-orbital transcranial alternating current stimulation (tACS) with perceptual learning to enhance visual function in a patient with cone dystrophy. We assessed visual acuity, Vernier acuity, and contrast sensitivity, and conducted a Tau-U analysis to evaluate the results. While the Study revealed promising improvements in several visual functions, particularly in the early stages of testing, the specific impact of tACS was not evident. Our findings suggest that perceptual learning may have the potential to improve visual perception in individuals with cone dystrophy. However, further Research with larger and more diverse populations is necessary to determine the true efficacy of peri-orbital tACS and to better understand the mechanisms underlying the observed improvements.
Journal Paper
The effect of the symbolic meaning of speed on implicit timing
Battaglini L., Khodami, A., Capizzi, M, Mioni, G
Timing & Time Perception, 2024
Abstract: It has been demonstrated that the stimulus’s features, including size, brightness, numerosity, and loudness, can affect the perception of subjective and explicit time. But, in a daily life situation, actual events presumably involve an implicit processing of time rather than an explicit processing, with some studies suggesting that the presentation of emotional stimuli before the target stimulus influences implicit timing. The present study aims to test the implicit component of temporal processing that the symbolic meaning of speed might influence. We used a time foreperiod task in which participants were first presented with a warning signal recalling the meaning of fast or slow speed, followed by the target. Our study shows significant main effects of the presented image cue and foreperiod effect. We observed faster reaction time when the target was preceded by a faster image compared to a slow image and in dependence of the factor of weight. Based on this, we conclude the symbolic meaning of speed can affect implicit timing by altering how the brain interprets temporal data.
Journal Paper
Comparing self-report vs. performance measures of attentional control and efficiency
Khodami, A., Battaglini L., Jansarvatan M., Kireeva S.,
NeuroSci, 2024
Abstract: The Attention Control Scale (ATTC) is a widely used self-report measure of attentional control capacities. However, research questions whether it accurately substitutes for objective attention control tasks. This study investigated ATTC’s correlation with the Attention Network Test (ANT) across alerting, orienting, and executive control networks. We also used the Inverse Efficiency Score (IES) as an additional factor to check ATTC using ANT. We administered 143 participants who completed the ATTC questionnaire and ANT behavioral test assessing network efficiencies. The results showed non-significant ATTC-ANT correlations across all networks. In an additional analysis, while the ATTC demonstrated factorial validity, subjective control was disconnected from actual attention regulation efficiency. A small male advantage emerged for executive control. Dissociations likely stem from attention complexity and method variances rather than overlap. The findings do not support the ATTC as a stand-alone proxy for performance-based measurement. Multifaceted assessments are essential for comprehensively capturing attentional control.