Will adjacent channel interference affect signal strength or just throughput?

[david_pay]

I was given a screenshot showing 3 APs in a conference setting and asked to determine how to solve the problem of "extremely slow" internet speed.  I suspect it is adjacent channel interference (ch. 6, 7 and 8 are used) but the signal level of -88 is a bit confusing.  Even with adjacent channels, shouldn't the signal strength be greater than -88  within 150' in an open room (no barriers)? 
Screenshot shows:
AP#1  Encryption: WPA2 Signal: -88  Noise: -94  2.4GHz  Ch: 6
AP#2  Encryption: WPA2 Signal: -88  Noise: -94  2.4GHz  Ch: 7
AP#3  Encryption: WPA2 Signal: -88  Noise: -94  2.4GHz  Ch: 8

[max_o_driscoll]

678 overlap significantly.
Either turn the power down so the sidebands don't  drown each other out (Must be some graphics on google images that make that clear)

or go for better separation :

1 6 11 which is a much better solution.

pic courtesy wikipedia by way of google...

https://en.wikipedia.org/wiki/List_of_WLAN_channels#/media/File:2.4_GHz_Wi-Fi_channels_(802.11b,g_WL...

[david_pay]

Thanks for your input. I agree that channels 1, 6 and 11 are preferred, assuming there is not other interference on those channels (still...much better then 6, 7, 8). However, with changing those channels increase the signal or just help to minimize the interference. Does adjacent channel interference lower the signal dBm?