Investigating differences between proper and common nouns using novel word learning

• ¹ Macquarie University, Sydney, Cognitive Science, Australia
• ² NHMRC Centre for Clinical Research Excellence in Aphasia Rehabilitation, Australia
• ³ IDEALAB International Doctorate for Experimental Approaches to Language and Brain, Germany
• ⁴ Newcastle University, School of Education, Communication and Language Sciences, United Kingdom

Empirical studies have shown higher rates of tip-of-the-tongue states for proper nouns, in comparison to common nouns, in non-brain-damaged speakers (e.g., Valentine & Moore, 1995), and higher retrieval failure rates for proper nouns relative to common nouns in people with aphasia (e.g., Semenza, 2009). Some authors suggest the source of these differences lies in logical properties (e.g., Semenza, 2009). That is, common nouns refer to a category of beings or objects that share certain semantic properties, while proper nouns designate specific individual beings or objects with unique features. Other authors attribute the distinction in processing to a number of statistical properties that differ across common and proper nouns (Kay, Hanley, & Miles, 2001). The aims of the present study were: 1) to dissociate the effects of logical and statistical properties by using novel words with equal statistical properties; 2) to determine whether people with aphasia show disproportionate impairments in learning proper nouns relative to common nouns, compared to aged-matched subjects. Methods We tested young (n=16) and elderly (n=14) adult non-brain-damaged participants and people with aphasia (n=2). Items-to-be-learnt were given as representatives of an unknown species (n=10) in the common noun condition, or as individual creatures (n=10) in the proper noun condition. The experiment consisted of 5 sessions. Each session included a learning phase and a test phase with naming and word-picture verification tasks. Results and Discussion Preliminary analysis showed learning of both common and proper nouns for both younger (F(4)=140.68, p<.01) and elderly (F(4)=34.87, p<.01) non-brain-damaged participants, with learning being significantly better for the younger group (F(4)=6.5, p<.01). Contrary to expectations, performance on proper nouns was better than that for common nouns for both young and elderly subjects (F(1)=6.47, p=.02 and F(1)=9.75, p<.01, respectively), possibly due to the different exemplars of each proper noun sharing more visual features than the different exemplars of each common noun. The two people with aphasia did not show any learning but their performance was not significantly different from the overall performance of elderly controls due to high variability within the latter group. Thus, previously shown difficulty in retrieving proper nouns particularly may be attributed to statistical differences (such as frequency, familiarity and age of acquisition) between proper and common nouns. As demonstrated in our study, these statistical properties being equal, no advantage in retrieval is observed for common nouns anymore.