Investigating Fast Mapping Task Components: No Evidence for the Role of Semantic Referent nor Semantic Inference in Healthy Adults

Abstract

Fast mapping (FM) is an incidental learning process that is hypothesized to allow rapid, cortical-based memory formation, independent of the normal, hippocampally dependent episodic memory system. It is believed to underlie the rapid vocabulary learning in infants that occurs separately from intentional memorisation strategies. Interest in adult FM learning was stimulated by a report in which adults with amnesia following hippocampal damage showed a normal ability to learn new object-name associations after an incidental FM task, despite their impaired memory under a conventional intentional memorization task. This remarkable finding has important implications for memory rehabilitation, and has led to a number of neuropsychological and neuroimaging studies in other patients and controls. Given this growing interest in adult FM, we conducted four behavioural experiments with healthy adults (N = 24 young or older adults in Experiments 1-3 using within-participant designs; N = 195 young adults in Experiment 4 using a between-participant design) that attempted to dissect which component(s) of the FM task are important for memory. Two key components of the FM task have been claimed to support FM learning: (1) provision of a known semantic referent and (2) requirement that the new association be inferred. Experiment 1 provided no evidence that removing the semantic referent impaired memory performance, while Experiment 2 provided no evidence that removing the semantic inference impaired performance. Experiment 3 was a replication of Experiment 2 with older participants, based on the hypothesis (from studies of amnesic individuals) that FM would be more effective following the hippocampal atrophy typical of increasing age, but again found no evidence that semantic inference is beneficial. Given potential concerns about contamination between tasks when each participant performed multiple variants of the FM task, we ran a final between-participant design in which each participant only ever did one condition. Despite 80% power and despite being able to detect better memory following intentional memorization in the explicit encoding (EE) control condition than in each of the FM conditions, we again found no evidence of differences between any FM conditions. We conclude that there is no evidence that the components hypothesized to be critical for FM are relevant to healthy adults.

Keywords: episodic encoding; fast mapping; hippocampus; learning; memory.

Figure 1

Original fast mapping (FM) procedure, FM variants, and explicit encoding (EE) conditions. Five conditions were implemented across four experiments. Experiments 1–3 tested three of these conditions, in separate study-test blocks, in within-participant designs. Experiment 4 tested all five conditions in a between-participant design. Experiment 1 used conditions FM, FM-r, and FM-ir; Experiment 2 was FM, FM-i, and FM-ir; Experiment 3 replicated the conditions and methods of Experiment 2, but in a healthy older group; Experiment 4 implemented FM, FM-r, FM-i, FM-ir, and EE in between-participants in young groups. For additional information on learning conditions, see main text. In the study phase for FM variants, names were to be incidentally associated with the unknown picture. Key prompts for “yes”/“no” were displayed at the bottom of the screen, on respective sides, but are omitted from this figure for simplicity. In the EE condition (administered in Experiment 4 only), participants were instructed to learn. The test phase, which was methodologically identical in all experiments and conditions, explicitly tested memory in a 3 Alternative Force Choice (3AFC) test. Study and test phases were separated by a 6–10 min nonverbal task. In Experiments 1–3, presentation order of learning condition and stimuli set-to-condition assignment was counterbalanced across participants within each experiment.

Figure 2

Memory performance in Experiments 1–3 from 3AFC at the test phase (chance = 0.33) for FM variants administered within-participant. Experiment 1 (light blue bars) shows memory performance for healthy young adults under FM, FM-r, and FM-ir; there were no significant differences between conditions. Experiment 2 (dark blue bars) shows memory performance for a different group of healthy young adults under FM, FM-i, and FM-ir. Significant differences are marked ** = p < 0.01, *** = p < 0.001. Experiment 3 (grey bars) shows performance of healthy older adults under same conditions as Experiment 2. Trending differences are marked + = p < 0.064. Mean performance is reported at the top of each bar. Error bars are standard error of the mean.

Figure 3

Analogous plot to Figure 2, except 3AFC memory test performance (chance = 0.33) is from the first study-test block only, for which participants were not aware of test phase.

Figure 4

Memory performance in Experiment 4 from 3AFC at the test phase (chance = 0.33) for FM variants and EE. Conditions were administered between-participant. Memory performance for healthy young adults under FM, FM-r, FM-i, and FM-ir did not significantly differ between conditions. All FM conditions significantly differed from the explicit learning condition, EE. Significant differences are marked * = p < 0.05, two tailed. Mean performance is reported at the top of each bar. Error bars are standard error of the mean.