Pitfalls in post hoc analyses of population receptive field data

Data binning involves grouping observations into bins and calculating bin-wise summary statistics. It can cope with overplotting and noise, making it a versatile tool for comparing many observations. However, data binning goes awry if the same observations are used for binning (selection) and contrasting (selective analysis). This creates circularity, biasing noise components and resulting in artifactual changes in the form of regression towards the mean. Importantly, these artifactual changes are a statistical necessity. Here, we use (null) simulations and empirical repeat data to expose this flaw in the scope of post hoc analyses of population receptive field data. In doing so, we reveal that the type of data analysis, data properties, and circular data cleaning are factors shaping the appearance of such artifactual changes. We furthermore highlight that circular data cleaning and circular sorting of change scores are selection practices that result in artifactual changes even without circular data binning. These pitfalls might have led to erroneous claims about changes in population receptive fields in previous work and can be mitigated by using independent data for selection purposes. Our evaluations highlight the urgency for us researchers to make the validation of analysis pipelines standard practice

Characterizing the population receptive fields of the hand dorsum and palm

Introduction: In an fMRI study, we explored the population receptive eld (pRF; Dumoulin & Wandell, 2008) properties of the voxels in the dorsum and palm area of the primary somatosensory region (area 3b). Behavioural studies adopting tactile discrimination tasks suggested that these two skin surfaces are represented differently, with the dorsum representation being more distorted than the palm representation (Longo & Haggard, 2011). Longo and Haggard (2011) explained these results by suggesting that the receptive elds of the dorsum surface are more elongated along the proximodistal hand axis than the ones of the palm – the pixel model. The authors based this idea mostly on animal studies (e.g. Alloway et al, 1989; Brooks et al, 1961; Brown et al, 1975). However, it is not clear if this is also the case for humans as, to the best of our knowledge, no study so far has investigated the pixel hypothesis systematically. Methods: The same participant was tested in two fMRI experiments (12 runs for experiment 1; 6 runs for experiment 2). In separate runs, the experimenter manually stimulated either the participant's dorsum or palm with an object (a circle covering 4 grid cells when centred at one intersection in experiment 1, a square covering one cell in experiment 2). A 4x4 grid (7 cm per side) was drawn on the participant's palm and dorsum (Figure 1). In experiment 1, the intersections of the grid lines were numbered from 1 to 25, whereas in experiment 2 each cell of the grid was numbered from 1 to 16. An acoustic cue instructed the experimenter on which skin region to stimulate and for how long. In experiment 1, we employed a random sequence in which each grid intersection was stimulated once per run interleaved with 7 randomly presented null trials. Each trial was 4 seconds and included the delivery of the touch on the instructed location plus small rotatory movements in anti-clockwise and clockwise directions. In experiment 2, we used an ordered sequence from 1 to 16 and back which was repeated 4 times in each run (2 null trials were presented every 4 trials). A tactile stimulation lasted for 2 seconds and consisted of 4 tactile events (~ 2Hz) in which the object gently touched the target skin location. We estimated the shape of the pRFs in anatomically and functionally predened regions of interests (see Figure 2A). To t the data, we used an oriented elliptical Gaussian with four parameters: the stimulated skin location (x and y); the long and short axes of the ellipse (σ1 and σ2), and the orientation (ϑ). We dened the anisotropy as the absolute value of the logarithm of the ratio between the horizontal and vertical axis. Orientations were transformed such that ellipses with the long axis running along the proximodistal orientation had an angle of 90 degrees. Results: Figure 2B shows the results for the voxel with the highest goodness of t for each of the skin surfaces stimulated in experiment 2. The green dot indicates the centre of the elliptical shape. The estimated pRF on the dorsum has a higher anisotropy than the one on the palm. Figure 2C shows the locations of all the estimated pRFs. In Figure 2D, we plotted each semi-major axis angle as an oriented line with the length proportional to the level of anisotropy. Ellipses oriented along the proximodistal axis of the hand appear vertical in the plot. The thick line indicates the resultant vector which gives an indication of the general orientation and anisotropy within the area. In both experiments, the dorsum showed higher anisotropy and both skin surfaces showed a slight deviation from the vertical orientation. Conclusions: In this study, we were able to estimate the pRF locations and shapes of the hand dorsum and palm. Our results suggest that many pRFs of the dorsum are oval-shaped and oriented along the proximodistal axis of the hand; the pRFs on the palm also show a similar characteristic, but less than dorsum. This provides some support for the pixel model (Longo & Haggard, 2011)

Influence of reward history on visual working memory representations

Reward is a strong determinant of human and non-human behavior, influencing the exploration of the world around us and our interactions with it. Interestingly, the impact of reward and reward-associated objects is not limited to strategic changes in approach behavior or attention deployment, but also extends to situations in which prioritizing processing of such objects is not necessarily advantageous for current goals. In spite of converging evidence for the automatic influence of reward on attentional deployment, less is known about the impact of reward on other cognitive processes. In this thesis I describe a first attempt to investigate the influence of reward in encoding and maintenance of visual representations in working memory. Throughout this thesis I argue that once objects have been associated with a positive outcome in past encounters, they are preferentially encoded and maintained in visual working memory (VWM) even when reward is no longer provided or when there is no consistent pairing between reward feedback and target identity. In Chapters 2 and 3 I demonstrate that reward associated objects interfere with the visual representations of less valuable items maintained in VWM. This interference was already present starting 10 ms from the offset of the memory display suggesting that valuable objects directly affected the encoding of less valuable items. This robust phenomenon was observed at different delays, both when reward-associated objects were task-relevant and when they were not, and was independent of object salience. However, the interference disappeared when task requirements for target selection increased suggesting that items with a positive reward history can effectively capture attention and interfere with VWM representations only when cognitive resources are not exhausted by the main task (Chapter 3). In the last study presented in this thesis I explored the possibility that reward could impact VWM beyond target selection and encoding, namely influencing the active maintenance process. To investigate this hypothesis I measured reward priming effects on event-related potential (ERP) indices of selective attention – the N2pc - and visual working memory maintenance – the CDA (contralateral delay activity). Results indicate that reward modulated CDA only, speaking for a discrete effect of reward on VWM maintenance. While the precise nature of such modulation is still unknown, these results suggest that reward history might influence the precision or the duration of visual representations maintained in VWM. Further studies are necessary to directly test this hypothesis, but these initial results suggest an interesting direction for future research in better characterizing the nature and extent of the influence of reward history on visual cognition

Reward associations impact both iconic and visual working memory

AbstractReward plays a fundamental role in human behavior. A growing number of studies have shown that stimuli associated with reward become salient and attract attention. The aim of the present study was to extend these results into the investigation of iconic memory and visual working memory. In two experiments we asked participants to perform a visual-search task where different colors of the target stimuli were paired with high or low reward. We then tested whether the pre-established feature-reward association affected performance on a subsequent visual memory task, in which no reward was provided. In this test phase participants viewed arrays of 8 objects, one of which had unique color that could match the color associated with reward during the previous visual-search task. A probe appeared at varying intervals after stimulus offset to identify the to-be-reported item. Our results suggest that reward biases the encoding of visual information such that items characterized by a reward-associated feature interfere with mnemonic representations of other items in the test display. These results extend current knowledge regarding the influence of reward on early cognitive processes, suggesting that feature-reward associations automatically interact with the encoding and storage of visual information, both in iconic memory and visual working memory

When the hole changes the pigeon

Blog post about a regression to the mean / circularity error in pRF analysis - and the story about why we retracted a Current Biology articl

Mobile Apps That Promote Emotion Regulation, Positive Mental Health, and Well-being in the General Population: Systematic Review and Meta-analysis

BackgroundAmong the general public, there appears to be a growing need and interest in receiving digital mental health and well-being support. In response to this, mental health apps (MHapps) are becoming available for monitoring, managing, and promoting positive mental health and well-being. Thus far, evidence supports favorable outcomes when users engage with MHapps, yet there is a relative paucity of reviews on apps that support positive mental health and well-being. ObjectiveWe aimed to systematically review the available research on MHapps that promote emotion regulation, positive mental health, and well-being in the general population aged 18-45 years. More specifically, the review aimed at providing a systematic description of the theoretical background and features of MHapps while evaluating any potential effectiveness. MethodsA comprehensive literature search of key databases, including MEDLINE (via Ovid), EMBASE (via Ovid), PsycINFO (via Ovid), Web of Science, and the Cochrane Register of Controlled Trials (CENTRAL), was performed until January 2021. Studies were included if they described standalone mental health and well-being apps for adults without a formal mental health diagnosis. The quality of all studies was assessed against the Mixed Methods Appraisal Tool. In addition, the Cochrane Risk-of-Bias tool (RoB-2) was used to assess randomized control trials (RCTs). Data were extracted using a modified extraction form from the Cochrane Handbook of Systematic Reviews. A narrative synthesis and meta-analysis were then undertaken to address the review aims. ResultsIn total, 3156 abstracts were identified. Of these, 52 publications describing 48 MHapps met the inclusion criteria. Together, the studies evaluated interventions across 15 countries. Thirty-nine RCTs were identified suggesting some support for the role of individual MHapps in improving and promoting mental health and well-being. Regarding the pooled effect, MHapps, when compared to controls, showed a small effect for reducing mental health symptoms (k=19, Hedges g=–0.24, 95% CI –0.34 to –0.14; P<.001) and improving well-being (k=13, g=0.17, 95% CI 0.05-0.29, P=.004), and a medium effect for emotion regulation (k=6, g=0.49, 95% CI 0.23-0.74, P<.001). There is also a wide knowledge base of creative and innovative ways to engage users in techniques such as mood monitoring and guided exercises. Studies were generally assessed to contribute unclear or a high risk of bias, or to be of medium to low methodological quality. ConclusionsThe emerging evidence for MHapps that promote positive mental health and well-being suggests promising outcomes. Despite a wide range of MHapps, few apps specifically promote emotion regulation. However, our findings may position emotion regulation as an important mechanism for inclusion in future MHapps. A fair proportion of the included studies were pilot or feasibility trials (k=17, 33%), and full-scale RCTs reported high attrition rates and nondiverse samples. Given the number and pace at which MHapps are being released, further robust research is warranted to inform the development and testing of evidence-based programs