A phenomenon process or mechanism that does not exist in nature but is believed to exist due to erroneous interpretation of data or theories

Artefact stems from the Latin 'something made with skill', but occasionally, in science, the major skill at stake is how to distinguish an artefact from a natural phenomenon. Artefacts have haunted the experimental sciences since the emergence of the latter, much before the term was introduced into English at the beginning of the nineteenth century. In biology, 'artefact' was first used to denote aberrations produced in histological specimens by the fixation methods used to prepare the tissue for microscopic examination. However, with time, it came to embrace many types and tokens of artificial constructs,1 either concrete or conceptual, which are confused with the real thing.

It is useful to distinguish two major classes of artefacts: technical (definitions 1,2) and conceptual, or interpretational (definitions 1,3). A harsh fixative or an unreliable stain leading to the appearance of an imaginary brain structure could be the cause of technical artefacts. Similar illusions may result from non-specific antibodies in an immunoblot, sloppy development of an autoradiogram, or tricky electrophysiological setups with a will of their own. Expert scientists come to master and prune the potential sources of artefacts in their trade, but new "methods and techniques generate new artefacts. For example, with more and more data analysis being relegated to fancy computer systems, the computers themselves become a source of technical artefacts before the data even reach the scientist. It takes a careful team leader to identify the problem (e.g. Katz etal. 1998).

A common potential source of interpretational artefacts is the so-called post hoc argumentation (post hoc ergo propter hoc, Latin for 'after this hence because of this'). Post hoc means arguing that because one event was correlated later in time with another, the second happened because of the first. This could sometimes be straightened out by performing "control experiments in which the order of events is altered or the suspected cause omitted from the protocol. For example, suppose we are tempted to conclude that a "receptor for the "neurotransmitter "glutamate in the "rat "hippocampus is phosphorylated ("protein kinase) as a consequence of learning to navigate in a "maze, because the receptor molecule appears phosphorylated after the experience; this might be a post-hoc artefact rather than a real consequence of the learning experience (e.g. see "criterion).

Interpretational artefacts could also result from lack of expertise in, or awareness of, a domain of knowledge that is relevant to the finding. This is a risk encountered especially, but definitely not solely, by investigators who shift from one field to another. A study of conditioning illustrates the case. In the first half of the last century, many operant conditioning paradigms ignored the species-specific behavioural repertoires of the experimental animals. This led to questionable conclusions.

Probably hundreds of Ph.D. theses interpreted the pecking of pigeons in a Skinner box as an "instrumen-tally conditioned response; however, pecking is an innate response, the pigeons emit it anyway, and the situation might not have been instrumental but rather "classical conditioning (Jenkins and Moore 1973). Similarly, over the years, cats were reported to be meticulously conditioned to emit stereotypic behaviours in order to escape from puzzle boxes; but some of the typical behaviours, such as rubbing the flank or head against a pole, were later pointed out as species-specific feline greeting reactions, emitted in response to the observer rather than conditioned by the escape (Moore and Stuttard 1979). Note that here the artefact is both technical (due to the improper design of the experiment, allowing the observer to affect the behavioural response of the "subject), and interpretational. The role of the observer is probably continued to be ignored to this day in many labs; it would be of interest to enquire how often an unexpected behaviour of a rat in a "maze reflects an artefact due to the introduction into the room of a new perfume or after-shave or an admiring visitor. "Anthropomorphism is another potential source of interpretational artefacts, confusing innate ("a priori) species-specific behaviours with higher-order cognitive faculties ("clever Hans, "Ockham's razor).

Interpretational artefacts could also be due to variables unknown in the discipline at the time that the interpretation is being attempted. An example is provided by a study of the effect of exploratory behaviour on hippocampal neurons. When rats are transferred to an unfamiliar environment they explore and learn it. It has been reported that such exploration is accompanied by hippocampal "plasticity, including persistent facilitation of evoked neuronal responses (Green et al. 1990). Although the basic finding was confirmed (Moser et al. 1994), it later became clear that the effect is much smaller than first reported. The reason: fluctuations of up to 2-3 °C in brain temperature, occurring during the exploratory activity, modify neuronal properties in vivo and account for a substantial part of the observed 'plasticity' (Andersen and Moser 1995). The aforementioned temperature effect and the resulting potential artefacts were not recognized at the time. In this case, the artefact was not a waste of intellect; its exploration led to new insights on the tricks of brain physiology. In other words, it is absolutely possible to learn even from artefacts.

Whether the suspected artefact is of the technical or the interpretational type, the first-law-of-the-artefact frequently holds: the more important is the message, the faster is the artefact exposed. Artefacts that lead to boring conclusions gain immortality in obscure journals. But if the news is smashing, for example, that specific memories can be transferred from one individual to another in brain extracts (Babich et al. 1965; Ungar and Oceguera-Navarro 1965), the scientific community does its best to sort the facts out, even ifthe causes of the artefact, or at least what appears to be an artefact to the contemporary eye, do not always become clear in the process (Byrne et al. 1966; Nicholls et al. 1967; Smalheiser et al 2001).

Selected associations: Anthropomorphism, Control, Red herring, Scoopophobia

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