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"When we talk about time, we frame it in terms of space", writes Daniel Cossins ( 6 July, p 32 ). Indeed, "we" do, and "time as space" is a common metaphor in many languages. It reflects the close link between the way the human brain processes spatial and temporal sequences. But it equally reflects …

Cossins suggests that people who speak different languages represent the passing of time in different ways – left to right in English and vertically in Mandarin speakers. Couldn't this just be due to the writing systems they use? How do speakers of Arabic, written from right to left, represent time?

Discussing superweeds, you say that hand weeding crops is effective, though costly ( 22 June, p 12 ). But it can be effective only for crops grown in narrow rows with wide spaces between rows that people can walk along. Otherwise the weeders will trample the crop. Some vegetables are grown like this. But here …

You report researchers encoding the Gettysburg Address in DNA ( 6 July, p 15 ). This reminded me of the pilot project I worked on in the late 60s at the British Museum Department of Printed Books, cataloguing part of its 18th-century newspaper collection into a machine-readable format. We shared the project and computer time …

Michael Le Page writes about work towards hearing aids that monitor the user's brainwaves to tell which voice they are trying to pay attention to ( 25 May, p 16 ). This is leaping to the roof without climbing the stairs. The more urgent, and easier, task would be to redesign hearing aids so that …

• The primary motor cortex is nearer the front of the brain than we showed it ( 22 June, p 34 ). • Still floating in a tin can: the Apollo 11 mission took 75 hours 49 minutes to get from Earth to lunar orbit ( 13 July, p 37 ).

Wong describes many reasons why analysing the nutrient composition of organic and non-organic food is difficult to do. Surely a better way to look at an organic diet would be to compare the health outcomes in groups that are made up of those who primarily consume organic food and of those who don't? I have …

I read Leah Crane's article on missions to Mars with great interest ( 15 June, p 38 ). But we hear little about the potential impact of rocket launches on the climate. Astronauts frequently remind us of the fragility of the atmosphere, but is sending them to space causing the damage they warn of?

So NASA has decided to create a "commercial destination" on the International Space Station where tourists could stay in the future, with the aim of facilitating for-profit space tourism ( 15 June, p 5 ). That sounds fun: who wouldn't love to see Earth from orbit and experience weightlessness? But the problem is that space …

Donna Lu reports that researchers have created a glass artificial intelligence ( 13 July, p 7 ). But their paper says only that they did computer simulations of what would happen to light inside such material. They modified the distribution of areas with different indices of refraction in the simulation until they got the simulated …