Remembering 1500 pictures: The right hemisphere remembers better than the left

Abstract

We hypothesized that the right hemisphere would be superior to the left hemisphere in remembering having seen a specific picture before, given its superiority in perceptually encoding specific aspects of visual form. A large set of pictures (N = 1500) of animals, human faces, artifacts, landscapes, and art paintings were shown for 2 s in central vision, or tachistoscopically (for 100 ms) in each half visual field, to normal participants who were then tested 1–6 days later for their recognition. Images that were presented initially to the right hemisphere were better recognized than those presented to the left hemisphere. These results, obtained with participants with intact brains, large number of stimuli, and long retention delays, are consistent with previously described hemispheric differences in the memory of split-brain patients.

Introduction

It is commonly thought that the human brain has a vast, perhaps unlimited, memory for pictures. This notion is based on a series of classic studies conducted in the 1960s and 1970s, where subjects viewed several hundred or even thousand of images, each image for just a few seconds, and were then tested, after variable delays (ranging from hours to several days), for their picture recognition. In these studies, memory was found to be close to perfect, with error rates estimates of just 2% in a study by Shepard (1967) or accuracy rates of individual participants ranging from 85 to 96% (Standing, 1973, Standing et al., 1970).

It is also well known that perceptual and cognitive abilities are not uniformly distributed in the human brain. For example, the speech output control system is genetically constrained to develop in the left hemisphere rather than in the right (Corballis, 1991). Similarly, the knowledge database based on semantic and verbal memory (containing facts and words) appears more dependent on processing in the left hemisphere (LH) than in the right hemisphere (cf. Caramazza and Shelton, 1998, Damasio et al., 1996, Gazzaniga, 1983). In contrast, the right hemisphere (RH) is known for its ability to process visual–spatial information, e.g. the metrics of space (Laeng, Chabris, & Kosslyn, 2003) and depth perception (Carmon and Bechtold, 1969, Danta et al., 1978), as well as color vision (Davidoff, 1976) and the control of visual attention (Corbetta et al., 1993, Heilman and Van Den Abell, 1980). Thus, the two hemispheres can be distinguished according to the various types of information processing or computations that they support. On the basis of such knowledge, one would likely conclude that the RH encodes the types of representations that seem most relevant for remembering specific visual information contained in pictures.

Several findings within the neurosciences are already consistent with this hypothesis that the RH is superior to the LH in remembering having seen a specific picture before. Neuroimaging studies have shown a RH’s specific role in memory for visual textures or pictures of faces (Kelley et al., 1998, McDermott et al., 1999, Wagner et al., 1998). Several neuroimaging studies have also revealed a RH’s role for the processing of specific visual form information (e.g., Garoff et al., 2005, Koutstaal et al., 2001, Simons et al., 2003). Reductions in brain activation can be seen in specific areas of the RH when the same exemplar is repeated compared to when a different exemplar from the same class is presented (Vuilleumier, Henson, Driver, & Dolan, 2002); such “adaptation” effects for specific visual forms can be as detailed as a reduced response to a particular viewpoint of the exemplar. Studies of patients with brain damage have shown that lesions to the LH can disrupt memory for pictures (Goldstein et al., 2004, Incisa della Rocchetta et al., 1995), but it appears that damage to the RH’s temporal lobe disrupts the memory of specific pictures of objects even more (De Renzi, 1968, Milner, 1968, Nunn et al., 1999, Vilkki, 1987, Whitehouse, 1981). Finally, studies with “split-brain” patients have indicated a RH’s memory superiority (Metcalfe, Funnell, & Gazzaniga, 1995) in recognizing specific patterns. When series of pictures of common scenes or faces were shown to these patients and then each hemisphere was tested for their recognition, the RH appeared to support a “literal” or “veridical” memory for pictures and an ability to reject “lures” or “decoys” whereas the LH frequently confused, as previously seen, novel pictures that were similar to the old ones or consistent with the events common to a particular scene (Phelps and Gazzaniga, 1992, Metcalfe et al., 1995). In these split-brain studies the stimuli were first studied in free vision for a few seconds and their recognition was then tested in the same session with lateralized, tachistoscopic (e.g., 150 ms), presentations of the studied items and of similar but foil items in a yes/no recognition paradigm.