The Challenge of Illusory Perception of Animals: The Impact of Methodological Variability in Cross-Species Investigation

Simple Summary

Research in neurobiology and ethology has given us a glimpse into the different perceptual worlds of animals. More recently, visual illusions have been used in behavioural research to compare the perception between different animal species. The studies conducted so far have provided contradictory results, raising the possibility that different methodological approaches might influence illusory perception. Here, we review the literature on this topic, considering both field and laboratory studies. In addition, we compare the two approaches used in laboratories, namely spontaneous choice tests and training procedures, highlighting both their relevance and their potential weaknesses. Adopting both procedures has the potential to combine their advantages. Although this twofold approach has seldomly been adopted, we expect it will become more widely used in the near future in order to shed light on the heterogeneous pattern observed in the literature of visual illusions.

Abstract

Although we live on the same planet, there are countless different ways of seeing the surroundings that reflect the different individual experiences and selective pressures. In recent decades, visual illusions have been used in behavioural research to compare the perception between different vertebrate species. The studies conducted so far have provided contradictory results, suggesting that the underlying perceptual mechanisms may differ across species. Besides the differentiation of the perceptual mechanisms, another explanation could be taken into account. Indeed, the different studies often used different methodologies that could have potentially introduced confounding factors. In fact, the possibility exists that the illusory perception is influenced by the different methodologies and the test design. Almost every study of this research field has been conducted in laboratories adopting two different methodological approaches: a spontaneous choice test or a training procedure. In the spontaneous choice test, a subject is presented with biologically relevant stimuli in an illusory context, whereas, in the training procedure, a subject has to undergo an extensive training during which neutral stimuli are associated with a biologically relevant reward. Here, we review the literature on this topic, highlighting both the relevance and the potential weaknesses of the different methodological approaches.

Healthy Advertising Coming to Its Senses: The Effectiveness of Sensory Appeals in Healthy Food Advertising

With increasing obesity rates and the daily overload of unhealthy food appeals, an important objective for advertising today is to promote healthy food consumption. According to previous research, sensory food advertisements referring to multiple senses—a combination of visual (sight), tactile (touch) and olfactory (smell) cues—evoke more positive sensory thoughts and, therefore, higher taste perceptions than advertisements referring to a single sense (e.g., only taste cues). However, this research only focused on sensory advertising for unhealthy food. The current research investigates how sensory advertising can promote healthy food. While multiple-sense ads for unhealthy food were shown to be more effective than single-sense ads, we find that, for healthy food, single-sense ads increase taste perceptions and advertising effectiveness compared to multiple-sense ads. In two laboratory experiments, we show a different underlying process for this effect—that is, single-sense ads evoke fewer negative thoughts than multiple-sense ads, which mediates the effect of single-sense versus multiple-sense ads on taste perceptions and advertising effectiveness. Moreover, we show that these effects occur not only for verbal ads but, importantly, also for visual ads, which are omnipresent today. This article closes with implications for theory and suggestions for food marketers, ad executives, and public policy.

Right Sizing: Sensory-Based Product Design Is a Promising Strategy to Nudge Consumers toward Healthier Portions

Research has shown that people consume more food when offered larger portions, and that reducing exposure to large food portions and packages could decrease the average daily energy consumed. In this context, our aim is to develop strategies to promote healthier eating behaviors by reducing portion selection and intake. The present research investigates the impact of different visual attributes of foods on quantity perception and portion selection. In the first study, we tested whether modifying the shape of a familiar food influenced the ideal portion size in adults. In the second study, we assessed the impact of shape, number of units, size, and color variety on a perceived quantity for a familiar multiunit product in children. Participants (N₁ = 70 adults, N₂ = 62 children) completed different picture-based computer tasks. As hypothesized: (1) adults selected a smaller ideal portion size for an elongated product than for wider and thicker shapes, and (2) children’s perception of food quantity was primarily driven by number of pieces, with smaller effects of size and elongation. Perceived quantity was not influenced by color variety. These findings suggest that it may be possible to reduce the size of food portions without negatively impacting perceived quantity, and to provide opportunities to nudge consumers towards smaller portions while maintaining satisfaction.

Do domestic dogs (Canis lupus familiaris) perceive the Delboeuf illusion?

In the last decade, visual illusions have been repeatedly used as a tool to compare visual perception among species. Several studies have investigated whether non-human primates perceive visual illusions in a human-like fashion, but little attention has been paid to other mammals, and sensitivity to visual illusions has been never investigated in the dog. Here, we studied whether domestic dogs perceive the Delboeuf illusion. In human and non-human primates, this illusion creates a misperception of item size as a function of its surrounding context. To examine this effect in dogs, we adapted the spontaneous preference paradigm recently used with chimpanzees. Subjects were presented with two plates containing food. In control trials, two different amounts of food were presented in two identical plates. In this circumstance, dogs were expected to select the larger amount. In test trials, equal food portion sizes were presented in two plates differing in size: if dogs perceived the illusion as primates do, they were expected to select the amount of food presented in the smaller plate. Dogs significantly discriminated the two alternatives in control trials, whereas their performance did not differ from chance in test trials with the illusory pattern. The fact that dogs do not seem to be susceptible to the Delboeuf illusion suggests a potential discontinuity in the perceptual biases affecting size judgments between primates and dogs.