Here is what Ramanujacharya says in this section of the Sri Bhashya, in the course of refuting the Advaita belief that we should believe that duality is unreal on the basis of scripture despite it contradicting what we perceive:
In cases of Scripture conflicting with Perception, Scripture is not stronger. The True cannot be known through the Untrue. With reference to the assertion (p. 24 ff.) that Perception, which depends on the view of plurality, is based on some defect and hence admits of being otherwise accounted for--whence it follows that it is sublated by Scripture; we ask you to point out what defect it is on which Perception is based and may hence be accounted for otherwise.--' The beginningless imagination of difference' we expect you to reply.--But, we ask in return, have you then come to know by some other means that this beginningless imagination of difference, acting in a manner analogous to that of certain defects of vision, is really the cause of an altogether perverse view of things?--If you reply that this is known just from the fact that Perception is in conflict with Scripture, we point out that you are reasoning in a circle: you prove the defectiveness of the imagination of plurality through the fact that Scripture tells us about a substance devoid of all difference; and at the same time you prove the latter point through the former. Moreover, if Perception gives rise to perverse cognition because it is based on the imagination of plurality, Scripture also is in no better case--for it is based on the very same view.--If against this you urge that Scripture, although based on a defect, yet sublates Perception in so far as it is the cause of a cognition which dispels all plurality apprehended through Perception, and thus is later in order than Perception; we rejoin that the defectiveness of the foundation of Scripture having once been recognised, the circumstance of its being later is of no avail. For if a man is afraid of a rope which he mistakes for a snake his fear does not come to an end because another man, whom he considers to be in error himself, tells him 'This is no snake, do not be afraid.' And that Scripture is founded on something defective is known at the very time of hearing Scripture, for the reflection (which follows on hearing) consists in repeated attempts to cognise the oneness of Brahman--a cognition which is destructive of all the plurality apprehended through the first hearing of the Veda.--We further ask, 'By what means do you arrive at the conclusion that Scripture cannot possibly be assumed to be defective in any way, while defects may be ascribed to Perception'? It is certainly not Consciousness--self-proved and absolutely devoid of all difference--which enlightens you on this point; for such Consciousness is unrelated to any objects whatever, and incapable of partiality to Scripture. Nor can sense-perception be the source of your conviction; for as it is founded on what is defective it gives perverse information. Nor again the other sources of knowledge; for they are all based on sense-perception. As thus there are no acknowledged means of knowledge to prove your view, you must give it up. But, you will perhaps say, we proceed by means of the ordinary empirical means and objects of knowledge!--What, we ask in reply, do you understand by 'empirical'?--What rests on immediate unreflective knowledge, but is found not to hold good when tested by logical reasoning!--But what is the use, we ask, of knowledge of this kind? If logical reasoning refutes something known through some means of knowledge, that means of knowledge is no longer authoritative!--Now you will possibly argue as follows: 'Scripture as well as Perception is founded on Nescience; but all the same Perception is sublated by Scripture. For as the object of Scripture, i.e. Brahman, which is one and without a second, is not seen to be sublated by any ulterior cognition, Brahman, i.e. pure non-differenced Consciousness, remains as the sole Reality.'--But here too you are wrong, since we must decide that something which rests on a defect is unreal, although it may remain unrefuted. We will illustrate this point by an analogous instance. Let us imagine a race of men afflicted with a certain special defect of vision, without being aware of this their defect, dwelling in some remote mountain caves inaccessible to all other men provided with sound eyes. As we assume all of these cave dwellers to be afflicted with the same defect of vision, they, all of them, will equally see and judge bright things, e.g. the moon, to be double. Now in the case of these people there never arises a subsequent cognition sublating their primitive cognition; but the latter is false all the same, and its object, viz., the doubleness of the moon, is false likewise; the defect of vision being the cause of a cognition not corresponding to reality.--And so it is with the cognition of Brahman also. This cognition is based on Nescience, and therefore is false, together with its object, viz. Brahman, although no sublating cognition presents itself.--This conclusion admits of various expressions in logical form. 'The Brahman under dispute is false because it is the object of knowledge which has sprung from what is affected with Nescience; as the phenomenal world is.' 'Brahman is false because it is the object of knowledge; as the world is.' 'Brahman is false because it is the object of knowledge, the rise of which has the Untrue for its cause; as the world is.'
There is in fact a hierarchy of Pramanas: Anumana only has authority over those things which cannot be known through Pratyaksha, and Sabda only has authority over those things which cannot be known through Pratyaksha or Anumana. That is why in another section of the Sri Bhashya, Ramanujacharya takes time to disprove Anumana-based arguments for the existence of Brahman, because it's only if Brahman cannot be known through Pratyaksha or Anumana that the Vedic statements about Brahman can have any authority:
Because Brahman, being raised above all contact with the senses, is not an object of perception and the other means of proof, but to be known through Scripture only; therefore the text 'Whence these creatures are born,' &c., has to be accepted as instructing us regarding the true nature of Brahman.--But, our opponent points out, Scripture cannot be the source of our knowledge of Brahman, because Brahman is to be known through other means. For it is an acknowledged principle that Scripture has meaning only with regard to what is not established by other sources of knowledge. ... The conclusion meanwhile is that, since Brahman does not fall within the sphere of the other means of knowledge, and is the topic of Scripture only, the text 'from whence these creatures,' &c., does give authoritative information as to a Brahman possessing the characteristic qualities so often enumerated. Here terminates the adhikarana of 'Scripture being the source.
This hierarchy of Pramanas is, incidentally, the source of the Purva Mimamsa doctrine of Arthavadas, which I discuss in my answer here.
On a side note, I wanted to address your point about the defects of perception. According to Visistadvaita, perception is actually never wrong, i.e. you only perceives that which exists, not that which does not exist. What we intuitively think of as "wrong perception" is really just "limited perception", as Ramanujacharya discusses in yet another section of the Sri Bhashya:
Those who understand the Veda hold that all cognition has for its object what is real; for.Sruti and Smriti alike teach that everything participates in the nature of everything else. In the scriptural account of creation preceded by intention on the part of the Creator it is said that each of these elements was made tripartite; and this tripartite constitution of all things is apprehended by Perception as well. The red colour in burning fire comes from (primal elementary) fire, the white colour from water, the black colour from earth--in this way Scripture explains the threefold nature of burning fire. In the same way all things are composed of elements of all things. The Vishnu Purâna, in its account of creation, makes a similar statement: "The elements possessing various powers and being unconnected could not, without combination, produce living beings, not having mingled in any way. Having combined, therefore, with one another, and entering into mutual associations--beginning with the principle called Mahat, and extending down to the gross elements--they formed an egg," &c. (Vi. Pu. I, 2, 50; 52). This tripartiteness of the elements the Sûtrakâra also declares (Ve. Sû. III, 1, 3).... That thing is similar to another which contains within itself some part of that other thing; and Scripture itself has thus stated that in shells, &c., there is contained some silver, and so on. That one thing is called "silver" and another "shell" has its reason in the relative preponderance of one or the other element. We observe that shells are similar to silver; thus perception itself informs us that some elements of the latter actually exist in the former. Sometimes it happens that owing to a defect of the eye the silver-element only is apprehended, not the shell-element, and then the percipient person, desirous of silver, moves to pick up the shell. If, on the other hand, his eye is free from such defect, he apprehends the shell-element and then refrains from action. Hence the cognition of silver in the shell is a true one. In the same way the relation of one cognition being sublated by another explains itself through the preponderant element, according as the preponderance of the shell-element is apprehended partially or in its totality, and does not therefore depend on one cognition having for its object the false thing and another the true thing. The distinctions made in the practical thought and business of life thus explain themselves on the basis of everything participating in the nature of everything else.... That holy highest Brahman--while producing the entire world as an object of fruition for the individual souls, in agreement with their respective good and ill deserts--creates certain things of such a nature as to become common objects of consciousness, either pleasant or unpleasant, to all souls together, while certain other things are created in such a way as to be perceived only by particular persons, and to persist for a limited time only. And it is this distinction--viz. of things that are objects of general consciousness, and of things that are not so--which makes the difference between what is called 'things sublating' and 'things sublated.'
