Novelty at second glance: A critical appraisal of the novel-object paradigm based on meta-analysis

Abstract

The study of consistent individual differences in behaviour has become an important focus in research on animal behaviour. Behavioural phenotypes are typically measured through standardized testing paradigms and one frequently used paradigm is the novel object test. In novel object tests, animals are exposed to new (unknown) objects and their reaction is quantified. When repeating trials to assess the temporal consistency of individual differences, researchers face the dilemma of whether to use the same or different ‘novel’ objects, since the same stimulus can result in habituation, while exposure to different objects can result in context-dependent responses. We performed a quantitative assessment of 254 effect sizes from 113 studies on novel-object trials to evaluate the properties of this testing paradigm, in particular the effect of object novelty and time interval between novel-object trials on estimates of individual consistency. We found an increase of sample sizes and an increase of estimates of repeatabilities with time. The vast majority of short-term studies (<one month) used different novel objects, while long-term studies (>one month) used either the same or different novel objects about equally often. The average estimate for individual consistency was r = 0.47 (short-term r = 0.52, long-term r = 0.44). Novelty, time interval between trials and their interaction together explained only 3% of the total heterogeneity. Overall, novelobject trials reliably estimate individual differences in behaviour, but results were very heterogeneous even within the same study species, suggesting susceptibility to unknown details in testing conditions. Most studies that measure novel-object responses in association with food label the trait as neophobia, while novel-object trials in a neutral context are labelled variously as boldness/shyness, exploratory behaviour or neophobia/neophilia. Neophobia/neophilia is also the term most specific to novel object presentations. To avoid ambiguity, we suggest object neophobia/neophilia as the most specific label for novel-object responses.

Fear of the new? Geckos hesitate to attack novel prey, feed near objects and enter a novel space

“…This is also reflected in our repeatability analysis which yielded a low repeatability of only 0.12. A meta-analysis looking at repeatability in novel object tests (both neophobia and neophilia) showed an average repeatability of 0.47 (Takola et al, 2021) while another study looking at repeatability in behaviour reports an average of 0.37 (Bell, Hankison, & Laskowski, 2009). Repeatability of responses towards novel objects and novel foods in corvids was calculated around 0.5 (Miller et al, 2022).…”

“…To properly assess the presence of neophobia, responses are compared to those towards familiar food (Greggor et al, 2015). To test object neophobia, individuals are confronted with a novel object close to familiar food within a familiar environment and the latency to eat compared to the control without the novel object is recorded (Greggor et al, 2015; Takola, Krause, Müller, & Schielzeth, 2021). Testing food and object neophobia within a familiar environment is important, because background familiarity (context) can affect the intensity of a neophobic reaction.…”

“…A study in the Aegean wall lizard ( Podarcis erhardii ) tested object neophobia by measuring the time it took lizards to consume food next to an unfamiliar object (De Meester et al, 2022). Other studies in lizards focused on neophilia, the attraction towards novelty (Takola et al, 2021). For example, object neophilia was tested in the Italian wall lizard ( P. siculus ) and the Geniez’s wall lizard (P. virescens) to quantify boldness.…”

Socio-ecological correlates of neophobia in corvids

“…1 Our response variable tested true food (and object) neophobia (i.e., fear of the appearance of the food), rather than dietary conservatism (i.e., latency to consume a novel food regularly in the diet). 51 We use the terms ''object neophobia'' and ''food neophobia'' as we specifically tested trials in a foraging context/near resources (i.e., familiar food)-recommended terminology outlined in Takola et al 52 We used a different color/ flavor of novel food (jelly) in each round, and only 20% of subjects touched the novel food, therefore latency to consume novel food was not an informative measure for within-and between-species comparisons. We pooled resources across labs with the aim of increasing sample sizes and species representation.…”

“…63 Furthermore, a recent meta-analysis found repeatability to novel objects was larger in short-term than long-term studies. 52…”