Long-term memory for categories and concepts in horses (Equus caballus)

Three horses (Equus caballus) with a history of performing cognitive tasks including discrimination learning, categorization, and concept use were tested to evaluate their long-term memory (LTM) in three experiments. In addition, use of LCD multi-displays for stimulus presentation was incorporated into cognition testing protocol for the first time with horses. Experiment 1 tested LTM for discrimination learning that originally occurred 6 years earlier. Five sets of stimuli were used and the two horses tested showed no decrement in performance on four of the sets; however, both horses did score below chance on one set. Experiment 2 examined long-term categorization recall 10 years after horses had demonstrated the ability to make stimulus selections based on shared characteristics within a given category. The horse tested for LTM after the decade-long interval immediately and consistently applied the previously learned categorization rule to not only familiar but also novel sets of stimuli. Experiment 3 tested another horse for LTM for a relative size concept. This horse had originally demonstrated concept rule use in order to select stimuli based on their relative size to one another. More than 7 years later and without further training, this horse reliably applied the previously established size concept to both familiar and novel sets of stimuli. These findings are the first reports of long-term categorical and conceptual memory in horses and are consistent with observations of domestic and wild horses, which indicate that behavioral and ecological events may be remembered for long periods of time. These studies also demonstrate the adaptive nature of horses with regard to their ability to generalize over several different testing conditions.     

Differential aspects of visual short and long-term memory

Abstract

This paper is concerned with the decomposition of visual imagery ability in subcomponents. Basically, it is assumed that visual imagery consists of several components which are relatively independent of spatial imagery components (Kosslyn, Brunn, Cave, & Wallach, 1984; Poltrock & Agnoli, 1986; Poltrock & Brown, 1984).

Theoretical assumptions on individual differences in visual imagery are formulated within a framework of general information processing principles. Based on the assumption that data and conceptually driven processes are involved in visual imagery, we turned to the question of whether vivid and non-vivid imagers differ on a primary data or conceptually driven processing level. To induce primary data-driven visual processes, unfamiliar visual patterns were used (Logie, 1986; Phillips, 1983). A visual long-term memory task (Marks, 1973) should involve primary conceptually driven visual processes.

The analysis of relationships between self-report measures of visual imagery ability (VVIQ; Marks, 1973; TVIC; Gordon, 1949) and visual memory performance measures, showed that vivid imagers prefer, when already on a primary data-driven processing level, visual coding strategies that might favour the long-term storage of information contained in real-life pictures.     

Color vision in horses (Equus caballus): deficiencies identified using a pseudoisochromatic plate test

In the past, equine color vision was tested with stimuli composed either of painted cards or photographic slides or through physiological testing using electroretinogram flicker photometry. Some studies produced similar results, but others did not, demonstrating that there was not yet a definitive answer regarding color vision in horses (Equus caballus). In this study, a pseudoisochromatic plate test--which is highly effective in testing color vision both in small children and in adult humans--was used for the first time on a nonhuman animal. Stimuli consisted of different colored dotted circles set against backgrounds of varying dots. The coloration of the circles corresponded to the visual capabilities of different types of color deficiencies (anomalous trichromacy and dichromacy). Four horses were tested on a 2-choice discrimination task. All horses successfully reached criterion for gray circles and demonstration circles. None of the horses were able to discriminate the protan-deutan plate or the individual protan or deutan plates. However, all were able to discriminate the tritan plate. The results suggest that horses are dichromats with color vision capabilities similar to those of humans with red-green color deficiencies.