Artifact Hypothesis Research Articles

Back to the original omnivore: On the artefactual nature of Peterson’s thesis of omnivorousness

Developed by Peterson in the early nineties, the thesis of omnivorousness involves a profound transformation of the principles thought to structure the distribution of cultural tastes and consumption. More specifically, this thesis posits that eclectic dispositions have replaced snobbish inclinations among high-status people. While the influence of this thesis has been important in the field over the past two decades, Peterson eventually questioned the reliability of the research literature dealing with omnivorousness. Notably, he raised the possibility that the thesis of omnivorousness may be grounded in a mere methodological artifact. In the present article, I examine such a possibility by focusing on potential flaws that may affect Peterson’s studies. Based on theoretical analyzes as well as empirical investigations, I point out the inconsistencies of Peterson’s operationalizations of omnivorousness, the poor association between taste and consumption in the data that the author mobilized, the arbitrariness of the musical hierarchies that he created, and the lack of validity of Peterson’s main findings regarding the dynamics of omnivorousness over time. All in all, this study supports the “artefact hypothesis” formulated by Peterson and invites investigators to be cautious when theorizing and contextualizing omnivorousness.

Subspecies description rates are higher in morphologically complex land snails

AbstractSubspecies richness (average number of subspecies per species = SSP/SP) has traditionally been explained by niche breadth, characteristics of the preferred habitat (“habitat hypothesis”), dispersal ability, range size (“range size hypothesis”), etc. However, in several invertebrate groups, there are striking differences between SSP/SP across families, which cannot be explained using classic arguments, and we might assume some hidden factor in the background. For example, some families of terrestrial molluscs, that possess conspicuously more subspecies than others, have higher degree of morphological complexity (shell size, number of diagnosable shell characters), for which we propose the “artefact hypothesis.” According to this, morphological complexity plays an important role in taxonomists' subspecies recognition. We used shell size, number of characters mentioned in species descriptions and area extent in six European land snail families, and habitat characteristics (rock‐dwelling vs. non‐rock‐dwelling) in one largest European snail families (Clausiliidae) to test our hypothesis. We found that all three factors (range size, morphological complexity and habitat type) correlated positively with the SSP/SP ratio. Although the generality of our findings has to be tested in other invertebrate phyla, we provide examples of striking differences between SSP/SP ratios in butterflies (Lepidoptera) and beetles (Coleoptera) as well. Our findings imply that researchers (a) should use the number of SSP more carefully in comprehensive studies, and (b) should maintain and use the rank subspecies in order to provide a stronger status for the species rank, and avoid taxonomic inflation. Furthermore, the subspecies rank might be more useful for “cryptic species” (clades that are indistinguishable morphologically) than species.

Is the Discrepancy between Numbers Derived from Verbal and Numerical Protocols for 9‐Point Hedonic Scales an Artifact of Product Choice?

AbstractPrior research showed that responses to the “numbers only” versions the 9‐point hedonic scale were not interchangeable with numbers assigned to responses to the “words only” versions of the scale. One explanation is that the discrepancy is artifactual, because the stimuli used in the experiments had been generally liked. Such stimuli tend to elicit responses to the “words only” version of the scale in the range from 5 to 9. For the “numbers only” version, scores are free to range across the whole scale. It was hypothesized that this artifact could explain the discrepancy in responses to the different versions of the scale. To investigate this, it was arranged for “words only” responses to fall in the range 1–4, by including products that were putatively disliked. This manipulation increased the range of scores for the “words only” scale into its lower portion, with a range of scores comparable to that for the “numbers only” scale. Yet, the data obtained from the two scales remained discrepant. This did not support the artifact hypothesis. Accordingly, the hypothesis that differences in cognitive strategy were the major explanation for the discrepancy was preferred.Practical ApplicationsThere are two versions of what is referred to as the 9‐point hedonic scale. One is the original “words only” version, such that numerical values are assigned to the verbal responses given on the scale. The second version is a purely numerical version, ranging 1–9, from which numerical responses are obtained directly. Prior research has shown that the numerical data derived from these versions are not interchangeable. Some sensory professionals do not specify which version of the scale they are using, so confusions can occur when making comparisons between different studies. As always, it is important to study the experimental variables involved with the use of these scales. Accordingly, it is pertinent to investigate the cause of the lack of interchangeability. Such research is important, because with the widespread use of the scale, it is likely that misleading comparisons between the data elicited by the two versions of the scale are likely to occur.

Excising stem samples underwater at native tension does not induce xylem cavitation.

Xylem resistance to water stress-induced cavitation is an important trait that is associated with drought tolerance of plants. The level of xylem cavitation experienced by a plant is often assessed as the percentage loss in conductivity (PLC) at different water potentials. Such measurements are constructed with samples that are excised underwater at native tensions. However, a recent study concluded that cutting conduits under significant tension induced cavitation, even when samples were held underwater during cutting. This resulted in artificially increased PLC because of what we have termed a 'tension-cutting artefact'. We tested the hypothesized tension-cutting artefact on five species by measuring PLC at native tension compared with after xylem tensions had been relaxed. Our results did not support the tension-cutting artefact hypothesis, as no differences were observed between native and relaxed samples in four of five species. In a fifth species (Laurus nobilis), differences between native and relaxed samples appear to be due to vessel refilling rather than a tension-cutting effect. We avoided the tension-cutting artefact by cutting samples to slightly longer than their measurement length and subsequent trimming of at least 0.5 cm of sample ends prior to measurement.

The standard centrifuge method accurately measures vulnerability curves of long-vesselled olive stems.

The standard centrifuge method has been frequently used to measure vulnerability to xylem cavitation. This method has recently been questioned. It was hypothesized that open vessels lead to exponential vulnerability curves, which were thought to be indicative of measurement artifact. We tested this hypothesis in stems of olive (Olea europea) because its long vessels were recently claimed to produce a centrifuge artifact. We evaluated three predictions that followed from the open vessel artifact hypothesis: shorter stems, with more open vessels, would be more vulnerable than longer stems; standard centrifuge-based curves would be more vulnerable than dehydration-based curves; and open vessels would cause an exponential shape of centrifuge-based curves. Experimental evidence did not support these predictions. Centrifuge curves did not vary when the proportion of open vessels was altered. Centrifuge and dehydration curves were similar. At highly negative xylem pressure, centrifuge-based curves slightly overestimated vulnerability compared to the dehydration curve. This divergence was eliminated by centrifuging each stem only once. The standard centrifuge method produced accurate curves of samples containing open vessels, supporting the validity of this technique and confirming its utility in understanding plant hydraulics. Seven recommendations for avoiding artefacts and standardizing vulnerability curve methodology are provided.

Vulnerability to cavitation in Olea europaea current‐year shoots: further evidence of an open‐vessel artifact associated with centrifuge and air‐injection techniques

Different methods have been devised to analyze vulnerability to cavitation of plants. Although a good agreement between them is usually found, some discrepancies have been reported when measuring samples from long-vesseled species. The aim of this study was to evaluate possible artifacts derived from different methods and sample sizes. Current-year shoot segments of mature olive trees (Olea europaea), a long-vesseled species, were used to generate vulnerability curves (VCs) by bench dehydration, pressure collar and both static- and flow-centrifuge methods. For the latter, two different rotors were used to test possible effects of the rotor design on the curves. Indeed, high-resolution computed tomography (HRCT) images were used to evaluate the functional status of xylem at different water potentials. Measurements of native embolism were used to validate the methods used. The pressure collar and the two centrifugal methods showed greater vulnerability to cavitation than the dehydration method. The shift in vulnerability thresholds in centrifuge methods was more pronounced in shorter samples, supporting the open-vessel artifact hypothesis as a higher proportion of vessels were open in short samples. The two different rotor designs used for the flow-centrifuge method revealed similar vulnerability to cavitation. Only the bench dehydration or HRCT methods produced VCs that agreed with native levels of embolism and water potential values measured in the field.

Recent advances in tree hydraulics highlight the ecological significance of the hydraulic safety margin

Drought-induced cavitation resistance varies considerably between tree species and forest ecosystems (Maherali et al., 2004; Delzon et al., 2010) and is closely linked to survival under severe drought in both conifers (Brodribb & Cochard, 2009; Brodribb et al., 2010) and angiosperms (Kursar et al., 2009; Anderegg et al., 2012; Barigah et al., 2013; Urli et al., 2013). Choat et al. (2012) recently reported that most trees operate very close to their threshold of cavitation, leaving them potentially vulnerable to drought-induced mortality in a warmer/drier world (Engelbrecht, 2012). Indeed, species growing in dry environments are more resistant to droughtinduced cavitation (more negative water potential at 50% cavitation, P50) but experience a more negative minimumwater potential (Pmin) than those growing in wet environments. The so-called hydraulic safety margin, the difference between the level of water stress experienced by a species in the field (Pmin) and the level of water stress leading to hydraulic failure, is, therefore, remarkably narrow, whatever the forest species and biome considered (Choat et al., 2012). This pattern provides clues to the global droughtinduced mortality currently observed, even in very wet environments, such as tropical forests (Allen et al., 2010). Klein et al. (2014) play down the functional significance of the hydraulic safety margin in the vulnerability of forests to drought, pointing out the important role played by additional mechanisms, such as the ability of trees to repair embolism. While it is obvious that drought-induced forest dieback is a complex process involving a number of biotic and abiotic factors, we would like to draw the attention of scientists to the state of evidence for embolism repair, thereby guiding research on tree drought resistance into the most relevant and fruitful directions

No evidence for an open vessel effect in centrifuge‐based vulnerability curves of a long‐vesselled liana (Vitis vinifera)

Vulnerability to cavitation curves are used to estimate xylem cavitation resistance and can be constructed using multiple techniques. It was recently suggested that a technique that relies on centrifugal force to generate negative xylem pressures may be susceptible to an open vessel artifact in long-vesselled species. Here, we used custom centrifuge rotors to measure different sample lengths of 1-yr-old stems of grapevine to examine the influence of open vessels on vulnerability curves, thus testing the hypothesized open vessel artifact. These curves were compared with a dehydration-based vulnerability curve. Although samples differed significantly in the number of open vessels, there was no difference in the vulnerability to cavitation measured on 0.14- and 0.271-m-long samples of Vitis vinifera. Dehydration and centrifuge-based curves showed a similar pattern of declining xylem-specific hydraulic conductivity (K(s)) with declining water potential. The percentage loss in hydraulic conductivity (PLC) differed between dehydration and centrifuge curves and it was determined that grapevine is susceptible to errors in estimating maximum K(s) during dehydration because of the development of vessel blockages. Our results from a long-vesselled liana do not support the open vessel artifact hypothesis.

The Hispanic Mortality Advantage and Ethnic Misclassification on US Death Certificates

We tested the data artifact hypothesis regarding the Hispanic mortality advantage by investigating whether and to what degree this advantage is explained by Hispanic origin misclassification on US death certificates. We used the National Longitudinal Mortality Study, which links Current Population Survey records to death certificates for 1979 through 1998, to estimate the sensitivity, specificity, and net ascertainment of Hispanic ethnicity on death certificates compared with survey classifications. Using national vital statistics mortality data, we estimated Hispanic age-specific and age-adjusted death rates, which were uncorrected and corrected for death certificate misclassification, and produced death rate ratios comparing the Hispanic with the non-Hispanic White population. Hispanic origin reporting on death certificates in the United States is reasonably good. The net ascertainment of Hispanic origin is just 5% higher on survey records than on death certificates. Corrected age-adjusted death rates for Hispanics are lower than those for the non-Hispanic White population by close to 20%. The Hispanic mortality paradox is not explained by an incongruence between ethnic classification in vital registration and population data systems.

Defining and Defending Murine Models of Plaque Rupture

There is general agreement that atherosclerotic plaque rupture is a major clinical problem and that finding ways to prevent it would be greatly facilitated by an animal model of plaque rupture. The article by Schwartz et al1 seeks to clarify and define the terms used in descriptions of disrupted atherosclerotic plaques, and then to apply these to murine models in order to assess their similarities to and differences from human ruptured lesions. On the face of it this seems a reasonable thing to do, but it has some serious conceptual problems. The first is the issue of whether it is useful at all to provide definitions of disrupted plaques, especially when these are based on histopathology. The second concerns the transferability of such definitions from human to mouse. I would like also to deal with issues relating to reevaluation of existing mouse models of plaque rupture. What do we gain from framing scientific definitions of real-world phenomena? In the context of the ruptured plaque, Schwartz et al1 argue that this would provide an agreed upon and consistent framework that would make it easier for different labs to compare and contrast their data. There is obviously virtue in this as a general principle in science, but we have to consider the possibility that in the developing field of plaque rupture it may be premature. We do not know why plaques rupture, we do not know whether “plaque erosions” are simply the adjacent manifestations of ruptures that are out of the plane of the section, and we do not know whether “plaque fissures” arise through a different set of processes to plaque ruptures. In other words, this means that we do not know whether ruptures, erosions and fissures are ontogenically similar or different. We are therefore moving beyond the boundaries …

Error negativity on correct trials: a reexamination of available data

The error negativity, an EEG wave observed when subjects commit an error in a choice reaction time (RT) task, is often considered as a sign of error detection. Recently, reports of Ne-like waves on correct responses did challenge this interpretation. It has been proposed, however, that these Ne-like waves result either from an artifactual contamination of response-locked activities by stimulus-locked ones, or from an implicit monitoring of the time elapsing during the RT. Our aim was to reprocess published data: (1) to compare the shape and amplitude of EMG-locked and stimulus-locked ERPs on correct trials, and (2) to compare the size of the EMG-locked Ne-like waves obtained on fast and slow trials. The results neither support the artifact hypothesis nor the RT monitoring one. Therefore, it seems that the Ne-like waves observed on correct trials do correspond to a Ne, which suggests that the Ne has a broader significance than just error detection.

Patterns of commonness and rarity in central European birds: reliability of the core‐satellite hypothesis within a large scale

The frequency distribution of species’ area of occupancy is often bimodal, most species being either very rare or very common in terms of number of occupied sites. This pattern has been attributed to the nonlinearity associated with metapopulation dynamics of the species, but there are also other explanations comprising sampling artifact and frequency distribution of suitable habitats. We tested whether the bimodal frequency distribution of occupied squares in central European birds could be derived solely from the frequency distribution of species population sizes (i.e. the sampling artifact hypothesis) or from the spatial distribution of their preferred habitats. Both models predict high proportion of very common species, i.e. the right side of frequency distribution. Bimodality itself is well predicted by models based on random placement of individuals according to their abundances but neither model predicts the observed prevalence of rare species. Even the combined models that assume random placement of individuals within the squares with suitable habitat do not predict such a high proportion of rare species. The observed distribution is more aggregated, rare species occupying a smaller portion of suitable habitat than predicted on the basis of their abundance. The pattern is consistent with metapopulation processes involving local population extinctions. The involvement of these processes is supported by two further observations. First, species rarity is associated with significant population trend and/or location on the edge of their ranges within central Europe, both situations presumably associated with metapopulation processes. Second, suitable habitats seem to be either saturated or almost unoccupied, which is consistent with the predictions of the metapopulation model based on nonlinear dynamics of extinction and colonization. Although the habitat suitability is an important determinant of species distribution, the rarity of many species of birds within this scale of observation seems to be affected by other factors, including local population extinctions associated with fragmentation of species’ habitats.

Melody lead in piano performance: expressive device or artifact?

As reported in the recent literature on piano performance, an emphasized voice (the melody) tends to be played not only louder than the other voices, but also about 30 ms earlier (melody lead). It remains unclear whether pianists deliberately apply melody lead to separate different voices, or whether it occurs because the melody is played louder (velocity artifact). The velocity artifact explanation implies that pianists initially strike the keys simultaneously; it is only different velocities that make the hammers arrive at different points in time. The measured note onsets in these studies, mostly derived from computer-monitored pianos, represent the hammer-string impact times. In the present study, the finger-key contact times are calculated and analyzed as well. If the velocity artifact hypothesis is correct, the melody lead phenomenon should disappear at the finger-key level. Chopin's Ballade op. 38 (45 measures) and Etude op. 10/3 (21 measures) were performed on a Bösendorfer computer-monitored grand piano by 22 skilled pianists. The hammer-string asynchronies among voices closely resemble the results reported in the literature. However, the melody lead decreases almost to zero at the finger-key level, which supports the velocity artifact hypothesis. In addition to this, expected onset asynchronies are predicted from differences in hammer velocity, if finger-key asynchronies are assumed to be zero. They correlate highly with the observed melody lead.

Axis I and Axis II disorders in alcoholics and drug addicts: fact or artifact?

It has been argued that Axis I and Axis II disorders diagnosed in substance users refer to substance-induced conditions rather than to independent psychiatric conditions; this argument will be referred to as the substance-related artifact hypothesis. Furthermore, Axis II symptoms co-occurring with Axis I disorders have been attributed to the contamination of personality assessment by mood and/or anxiety state effects (the trait-state artifact hypothesis). The present study is the first to prospectively examine the validity of these two hypothesized "artifacts" in substance users. In 276 individuals (57.6% female) applying for substance use treatment, current substance use disorders, mood/anxiety disorders and Axis II disorders were diagnosed using semistructured interviews both at baseline and at 1-year follow-up. The substance-related artifact hypothesis is tested by examining the covariation between recovery from substance use disorders on the one hand and recovery from and/or improvement of mood/anxiety and Axis II disorders on the other hand. The trait-state artifact hypothesis is tested by examining the covariation between recovery from mood/anxiety disorders on the one hand and recovery from and/or improvement of Axis II disorders on the other hand. Recovery from substance use disorders covaried with recovery from and improvement of mood/anxiety disorders, but not with recovery from or improvement of Axis II pathology. Furthermore, recovery from mood/anxiety disorders covaried with recovery from and improvement of personality disorders, in particular Cluster C disorders. Results from this study suggest that mood/anxiety disorders, but not personality disorders, diagnosed among people with substance use disorder may partly reflect substance-related artifacts. Furthermore, this study provides evidence for the contention that semistructured interview assessment of Axis II, at least without inquiry on an item-by-item basis, is susceptible to contamination by mood/anxiety state effects.

Primate theory of mind is a Turing test

Heyes's literature review of deception, imitation, and self-recognition is inadequate, misleading, and erroneous. The anaesthetic artifact hypothesis of self-recognition is unsupported by the data she herself examines. Her proposed experiment is tantalizing, indicating that theory of mind is simply a Turing test.

On size and area: Patterns of mammalian body size extremes across landmasses

We describe a biogeographic pattern in which mammalian body size extremes scale with landmass area. The relationship between the largest and the smallest mammal species found on different landbridge islands, mountaintops and continents shows that the size of the largest species increases, while that of the smallest species decreases, with increase in the area of the landmass. We offer two possible explanations: (1) that the pattern is the result of sampling artefacts, which we call the ‘statistical artefact hypothesis’, or (2) that the pattern is the result of processes related to the way body size affects the number of individuals that a particular species can pack in a given area, which we call the ‘area-scaling hypothesis’. Our results point out that the pattern is not a statistical artefact resulting from random sampling, but can be explained by considering the scaling of individual space requirements and its effect on population survival on landmasses of different area.

Independent Paths in the Development of Infant Learning and Forgetting

We investigated the possibility that age differences in infants’ long-term retention are artifacts of correlated differences in learning rates or learning opportunities (overlearning). Using path analytic procedures, these possibilities were examined in two experiments in which 15- and 18-month-olds (Experiment 1) and 12- and 15-month-olds (Experiment 2) learned five novel activities to a strict acquisition criterion. Three months later, infants’ retention was tested using four test trials with no further study opportunities. Using a series of causal models to test the relationships between age, learning rate, learning opportunities, and forgetting rate, the results disconfirmed the artifact hypothesis. These analyses indicated that, at least for criterion-learning designs, developmental declines in forgetting rates between 12 and 18 months of age do exist independent of developmental differences in learning. Furthermore, age differences in forgetting rates are not confounded with age differences in “overlearning.” These findings are discussed in terms of the growing body of evidence that attests to the continuity of memory development across childhood.

Sizing emboli in blood using pulse Doppler ultrasound--I: Verification of the EBR model.

An experiment to verify a theory describing ultrasound backscattering from emboli in flowing blood is presented. The theoretical predictions for the backscattered power versus embolus size are based on the measurement of the embolus to blood ratio (EBR) of backscattered acoustic power. This tool is necessary for in vivo clinical application because it removes the need to characterize attenuation and reflection loss in heterogeneous tissue. The experiment presented utilizes a customized ultrasound pulse Doppler that is capable of interrogating a sample volume with two different frequencies concurrently. A flow circuit including a 3.6-mm-diameter conduit in polyacrylamide gel in which emboli are observed with the dual frequency Doppler is described. The flow within the circuit has acoustic backscatter coefficient similar to blood due to a calibrated concentration of 31.1-mu diameter polystyrene microspheres. Polystyrene microsphere "emboli" having nominal diameters of 161 and 239 mu are placed in this flow loop and time series Doppler shift signatures are recorded. These signatures are investigated and a refraction artifact hypothesis is proposed to explain systematic deviation of the signatures away from theoretically expected results. Results show that gross discrimination of embolus size is feasible.

Learning rate, learning opportunities, and the development of forgetting.

Reported developmental declines in forgetting rates may be artifacts of correlated individual differences in learning rates or in the number of learning opportunities that children receive. This possibility was investigated in 2 experiments by using causal models that implemented possible relationships among age, forgetting rates, learning rates, and learning opportunities. The artifact hypothesis was disconfirmed. Forgetting rates declined markedly between early and late childhood when individual differences in learning rates and learning opportunities were factored out. The results were interpreted in terms of fuzzy-trace theory's proposals about the development of verbatim and gist memory systems

Question Form and Context Effects in the Measurement of Partisanship: Experimental Tests of the Artifact Hypothesis

Previous articles in this Review, including a Controversy in 1992, debated the comparability of alternative forms of the question about partisanship asked in Gallup and Michigan SRC surveys. Bishop, Tuchfarber and Smith contribute to this debate by reporting and analyzing evidence from 15 experimental surveys in Ohio in 1991–1993. They conclude that the distribution of partisan loyalties will generally be the same whether one uses the Gallup or Michigan Survey Research Center question and that, contrary to findings of Abramson and Ostrom, the Gallup form is no more responsive to short-term political forces than its SRC counterpart. In response, Abramson and Ostrom agree that during many time periods there will be little difference between aggregate levels of macropartisanship regardless of which measure is used. But they argue that during periods of political volatility the Gallup approach will accentuate differences, while the SRC version will attenuate them.