Visual short-term memory for global motion revealed by directional and speed-tuned masking Andrea Pavan n , Dominik Langgartner, Mark W. Greenlee Universit¨ at Regensburg, Institut f¨ ur Psychologie, Experimental and Clinical Neuroscience Study Programme, Universit¨ atsstr. 31, 93053 Regensburg, Germany article info Article history: Received 3 January 2013 Received in revised form 2 February 2013 Accepted 8 February 2013 Available online 27 February 2013 Keywords: Visual short-term memory Global motion Visual masking Direction selectivity Speed selectivity abstract Neurobehavioral research with non-human primates has shown that different attributes of motion stimuli, such as direction and speed can be stored in visual short-term memory (VSTM) with a high degree of accuracy. We examined VSTM for global motion with a memory masking paradigm to determine which stimulus attributes are important in the storage process. We presented in two visual quadrants global motion random dot kinematograms (RDKs), whereas in the two remaining visual quadrants we presented random-motion RDKs. This pattern of stimulation was displayed in two distinct temporal intervals, i.e., sample and test stimuli (duration: 200 ms), separated in time by a 3.2-s delay period. During the delay period a random- or directional-motion mask was presented briefly (200 ms) either at the beginning, in the middle or at the end of the delay period. The results showed that the mask mainly interferes with performance when displayed 200 ms after the offset of the sample and when it had a coherent direction rather than random directions. Moreover, the mask is significantly more effective when its direction and speed matched that of the remembered sample. These results support the notion that the memory representation of global motion is selective for direction and speed, being compromised by intervening directional stimuli presented immediately after the encoding phase. Moreover, this selectivity suggests that the same neural mechanisms involved in the processing of global motion may be recruited for its storage. & 2013 Elsevier Ltd. All rights reserved. 1. Introduction Visual short-term memory (VSTM) reflects the ability of the brain to (briefly) retain visual information to be subsequently used to guide ongoing actions (Baddeley, 1986; McKeefry, Burton, & Vakrou, 2007; Pasternak & Greenlee, 2005). There is neurophy- siological and psychophysical evidence that VSTM is selective for many attributes of a stimulus such as orientation, texture, con- trast, spatial frequency, motion direction and speed (Bisley & Pasternak, 2000; Bisley, Zaksas, Droll, & Pasternak, 2004; Bisley, Zaksas, & Pasternak, 2001; Magnussen & Greenlee, 1992, 1999; Magnussen, Greenlee, Asplund, & Dyrnes, 1991; Pasternak & Zaksas, 2003; Zaksas, Bisley, & Pasternak, 2001; for a review, see: Pasternak & Greenlee, 2005), moreover, it seems that these stimulus dimensions are stored by a series of parallel perceptual mechanisms with independent but limited processing resources (Magnussen, 2000). This hypothesis is also supported by a series of studies on visual priming (Campana, Cowey, Casco, Oudsen, & Walsh, 2007; Campana, Cowey, & Walsh, 2002, 2006; Campana, Pavan, & Casco, 2008), which showed that implicit short-term memory for simple stimulus attributes relies on the same low- level areas that are responsible for the analysis and representa- tion of such attributes. For example, Campana et al. (2002, 2006) using rTMS found that the disruption of area V5/MT selectively abolished priming for motion direction of coherently moving patterns, but it had no effect on priming for spatial position, which in turn is strictly dependent on the functional integrity of the left frontal eye field (FEF; Campana et al., 2007). Overall these studies support the notion that the neural mechanisms involved in the short-term memory of specific visual features are respon- sible also for their analysis (Bisley & Pasternak, 2000; Gibson & Maunsell, 1997; Magnussen, 2000; Magnussen & Greenlee, 1999; Pasternak & Greenlee, 2005). Most of the evidence in support of feature-selective retention mechanisms comes from behavioral studies that used memory- masking in conjunction with tasks involving delayed discrimina- tion of basic stimulus features (Pasternak & Greenlee, 2005). In such paradigms an irrelevant stimulus (i.e., memory mask) is introduced in the temporal delay between sample and test stimuli. Intervening masking stimuli have been shown to inter- fere with the (short-term) memory representation and produce a decrease in delayed discrimination performance. Moreover, by varying the properties of the masking stimuli it is possible to assess the properties of the remembered stimulus. Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/neuropsychologia Neuropsychologia 0028-3932/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.neuropsychologia.2013.02.010 n Corresponding author. Tel.: þ49 941 943 3582. E-mail address: andrea.pavan@psychologie.uni-regensburg.de (A. Pavan). Neuropsychologia 51 (2013) 809–817