May be this article will be useful.

 http://www.performancescience.org/ISPS2009/Proceedings/Rows/028Carvalheiro.pdf

Yes memory span is clearly different over sensory modes and many other factors. For example verbal span is often longer than spatial span. Non-phonological items are somewhat difficult to calibrate or describe in equivalent terms. 

The aging effect is somewhat controversial in the sense that many studies are not careful about excluding illness which is confounded with old age. However the consensus view is that aging reduces both verbal and non-verbal spans. It would be difficult to talk about an interaction since normally it is difficult to equate the two types of sequences!

Best of luck.

 Modality is not enough to quantify how many items a person can remember. There is also the person's experiences with the items. For instance, if the person is an expert in automobiles then the person will be able to remember many more automobiles in a memory battery than a person who is not. The same goes for both audio and visual items. I am not aware of the effects of tactile and expertise, but I'm sure that there has been some work on that. I would look up the work of Anders Ericsson. He has done numerous studies on memory span and expertise. https://psy.fsu.edu/faculty/ericsson.dp.html

Hi Asheek,

Nelson Cowan has discussed the notion of a general 4-chunk limit regardless of modality/stimulus-domain (see also the commentaries that follow his target paper):

Cowan, N. (2001). Metatheory of storage capacity limits. Behavioral and brain sciences, 24(01), 154-176.  http://langint.pri.kyoto-u.ac.jp/ai/intra_data/NobuyukiKawai/Kawai-Matsuzawa-Magical_number_5_in_a_chimpanzee.pdf    (note that content of this address-name is incorrect but the paper it links to is the right one)

With regard to sensory modality (visual vs auditory in particular) you may be interested in a paper we recently published showing that it's not the modality of items per se that's important but the different forms off perceptual organisation that stimuli from different sensory modalities afford (Macken et al., 2016, Cognition: http://orca.cf.ac.uk/92406/1/Macken%20et%20al%202016.pdf)

Hope that helps a bit,

All the best with your research,

Rob

Dear Asheek,

I hope that this paper might be useful to you. Good luck!

https://www.researchgate.net/publication/254110795_M_capacity_as_a_lifespan_construct_A_study_of_its_decrease_in_ageing_subjects

Article M capacity as a lifespan construct: A study of its decrease ...